The Safe Use of Laboratory Ducted Fume Cupboards - May 2011 Review every 2 years Occupational Health and Safety Service HSD029C (rev 2)
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May 2011 Review every 2 years The Safe Use of Laboratory Ducted Fume Cupboards Occupational Health and Safety Service HSD029C (rev 2)
Table of Contents
1 INTRODUCTION .............................................................................................................. 1
2 LEGISLATION ................................................................................................................. 1
3 MINIMUM DESIGN SPECIFICATION FOR FUME CUPBOARD SYSTEMS .................... 1
3.1 Safety and System Performance ............................................................................................... 1
3.2 Fume Cupboard Basics ............................................................................................................. 2
3.3 Fume Cupboard Types .............................................................................................................. 3
3.3.1 Constant Volume Fume Cupboards ................................................................................... 3
3.3.2 Variable Air Volume Fume Cupboards ............................................................................... 3
3.3.3 Recirculatory Fume Cupboards .......................................................................................... 4
3.3.4 High Efficiency Particulate Air (HEPA) Filtered Cabinets ................................................... 4
3.3.5 Microbiological Safety Cabinets / Laminar Flow Fume Cupboards .................................... 4
4 SAFE USE OF FUME CUPBOARDS ............................................................................... 4
4.1 The Purpose of a Fume Cupboard ............................................................................................ 4
4.2 Risk Assessment ....................................................................................................................... 5
4.3 How to Use a Fume Cupboard .................................................................................................. 5
4.4 Fume Cupboard Limitations ....................................................................................................... 8
4.5 The Fume Cupboard as a Storage Device ................................................................................ 8
4.5.1 Fume Cupboards Actively in Use for Experimentation ....................................................... 8
4.5.2 Fume Cupboards not in Active Use .................................................................................... 9
4.6 Shared Use of Fume Cupboards ............................................................................................... 9
4.7 Common Fume Cupboard Myths ............................................................................................... 9
5 TESTING AND MAINTENANCE ...................................................................................... 9
5.1 Frequency of Maintenance ........................................................................................................ 9
5.2 Responsibilities ........................................................................................................................ 10
6 FUME CUPBOARD PERFORMANCE TESTING ........................................................... 11
6.1 Frequency of Testing ............................................................................................................... 11
6.2 Record Keeping ....................................................................................................................... 11
6.3 Test Principles ......................................................................................................................... 11
6.3.1 Flow Visualisation Test ..................................................................................................... 11
6.3.2 Face Velocity Test ............................................................................................................ 11
6.3.3 Containment Test ............................................................................................................. 12
References and Further Reading ....................................................................................... 13
Appendix 1 - Fume Cupboard Pre-Use Operator Checklist ............................................. 14
Appendix 2 - Fume Cupboard Label .................................................................................. 15
Appendix 3 - Fume Cupboard Maintenance Schedule ..................................................... 16
Appendix 4 - Record of Examination and Test of Laboratory Fume Cupboard.............. 17
Appendix 5 - Face Velocity Test ........................................................................................ 19
Appendix 6 - Glossary of Terms ........................................................................................ 21
Acknowledgements ............................................................................................................ 221 INTRODUCTION
Fume cupboard systems are the most common control measure employed within the University for the
prevention of exposure to hazardous substances. The legislation governing their use and the
understanding of how they arrest and contain contaminants has developed significantly over the last
few years. It is the intention that this code of practice and guidance will establish a common operating
policy throughout the University in order to meet all statutory obligations.
This code of practice and guidance is for anybody whose work involves using a fume cupboard and for
those with delegated duties in departments such as the Departmental Safety Officer, Biological Safety
Officer and Radiation Protection Supervisor.
This document does not cover the use of laminar flow cabinets or microbiological cabinets, however
limited guidance is included on the use of recirculating fume cupboards and HEPA filtered chemical
powder handling cabinets (see section 3).
2 LEGISLATION
There are explicit requirements in the Control of Substances Hazardous to Health Regulations (as
amended) to prevent exposure of employees (and others who might be affected) to hazardous
substances, and where this is not possible, to adequately control exposure. The law also requires the
assessment of these hazards and risks and identification of measures to prevent or control them
before work is carried out.
Where necessary control can be achieved by measures such as local exhaust ventilation (LEV): the
classification of mechanical ventilation devices in which laboratory fume cupboards are placed.
The regulations establish the requirement for LEV systems to be maintained in an efficient state,
efficient working order, good repair and clean condition. They are also subject to thorough
examination and testing at periods not greater than fourteen months, and more frequently if the
assessment identifies higher risk. There is a specific requirement for users of fume cupboards to make
weekly checks of certain functions of the system, and to report any faults to management as soon as
is reasonably possible.
In addition, the design and manufacture of fume cupboards is controlled and regulated by British
Standards (BS 7258, Parts 1, 2, 3 and 4 – which apply to fume cupboards installed in the work place
prior to 2004, and BS EN 14175, Parts 1, 2, 3, 4, 5 and 6 for fume cupboards installed from 2004).
3 MINIMUM DESIGN SPECIFICATION FOR FUME CUPBOARD SYSTEMS
3.1 Safety and System Performance
A fume cupboard is a key protective and control device in laboratories where chemicals are used. It is
primarily a protective ventilated enclosure (partial containment device) designed such that hazardous
concentrations of quantities of airborne contaminants are prevented from escaping from the fume
cupboard into the work room or laboratory by means of a protective air barrier between the user and
the materials placed within the enclosure.
Potentially dangerous or obnoxious fumes must be efficiently conveyed from the fume cupboard
enclosure to an outside discharge point where they can be safely dispersed at low concentrations. In
so doing, the susceptibility to form an explosive or hazardous atmosphere inside the work space is
also reduced.
The fume cupboard is ventilated by an induced flow of air through an adjustable working opening
(namely the sash) which also offers the user some degree of mechanical protection against splashes
of substances and flying particles.
If anything interferes with the protective air barrier or the fume cupboard, or disrupts the air flow into
and within the fume cupboard, the fume cupboards ability to protect the user may be seriously
reduced.
The design and manufacture of fume cupboards is specified in the relevant British and European
Standards. Further information is available from Estate Management who must be consulted on the
1selection and installation of new fume cupboards, to ensure that all relevant parts of the British and
European Standards are complied with.
3.2 Fume Cupboard Basics
A well-designed fume cupboard, when properly installed and maintained, can offer a substantial
degree of protection to the user, provided that it is used appropriately and its limitations understood.
The common parts of a fume cupboard and their major functions are as follows:
Figure 1: Basic fume cupboard
Fume Cupboard Body -- The visible part of the fume cupboard that serves to physically contain
hazardous gases and vapours. The materials of construction of the cupboard body can vary
considerably and will depend on the intended use of the fume cupboard.
The most common materials used are solid epoxy resin for work surface and liners, toughened glass
for the sash and baffles. For special applications, stainless steel can be used where there is a high fire
risk; a ceramic work surface for regular use of corrosive liquids and; polypropylene work surface and
transparent PVC sash for hydrofluoric acid.
Baffles -- Panel or panels located within the fume cupboard which aid in distributing the air moving
into and through the cupboard. Baffles keep the airflow uniform across the cupboard opening, thus
eliminating dead spots and optimising capture efficiency. It is important that the baffles are not
obstructed as this effectively blocks the exhaust path.
Sash -- The transparent screen between the user and work place that can be adjusted vertically
and/or horizontally. Each fume cupboard should be marked with the optimum sash height, also known
as the normal sash working height. The sash should be held in this position when work involving the
fume cupboard is being performed and closed completely when the fume cupboard is not in use or is
left unattended. Modern fume cupboards are fitted with stops or other devices to prevent the normal
sash working height being exceeded. It is worth noting that the sash provides some protection to the
operator against splashing and minor explosions.
Airfoil (or bevelled frame/sill) -- Found along the bottom and side edges of the fume cupboard. Airfoils
streamline airflow into the fume cupboard, preventing the creation of turbulent eddies (due to sharp
edges) that can carry vapours out of the fume cupboard. The space below the bottom airfoil provides a
source of room air for the fume cupboard when the sash is fully closed.
Work surface -- Slab or platform which acts as the base of the fume cupboard’s workspace.
Generally, it is a flat surface with a raised edge around the periphery, known as an anti-spill lip. Sinks
are usually incorporated into the work surface and are positioned to the rear of the fume cupboard.
The work surface may be made from plastic materials, ceramics, cast epoxy, metals etc dependant
upon intended use.
Exhaust plenum / extract duct work -- All ductwork and associated equipment installed between the
point of connection to the fume cupboard and point of discharge. Materials such as paper towels
drawn into the plenum can create turbulence in this part of the fume cupboard, resulting in areas of
poor airflow and uneven performance.
2Face -- The imaginary plane running between the bottom of the sash to the work surface. Fume
cupboard face velocity is measured across this plane and is defined as the velocity of air passing
through the working aperture measured in the plane of the sash.
3.3 Fume Cupboard Types
There are several different types of fume cupboard ranging from simple ‘box’ types to sophisticated
‘aerodynamic’ types. These in turn can be constant volume cupboards or variable air volume
cupboards.
3.3.1 Constant Volume Fume Cupboards
In most fume cupboard installations, the exhaust flow rate or quantity of air pulled through the
cupboard is constant, hence the term ‘constant volume fume cupboard’. When the sash is lowered and
the cross-sectional area of the cupboard opening decreases the velocity of airflow (face velocity)
through the cupboard increases proportionally. By using the sash to adjust the front opening, it is
possible to adjust the airflow across the fume cupboard to the point where capture of contaminants is
maximized. This type of fume cupboard can be further subdivided into:
Conventional fume cupboards – these represent the original and most simple of fume
cupboard design styles. With a conventional fume cupboard, the volume of air exhausted is
constant, regardless of sash height. Since face velocity changes dramatically with sash
position, it is particularly important when working with conventional fume cupboards to
maintain the sash at its optimal height since this system will create higher air velocities as the
sash opening is decreased to the point of creating turbulence at the fume cupboard face. The
-1
optimal height (usually 50 cm) represents the point where the face velocity equals 0.5 ms .
Bypass fume cupboards – have an air bypass incorporated above the sash (identified by an
air make-up grille) which provides an additional source of room air when the sash is closed (ie
room air is able to flow into the fume cupboard by a route other than through the sash
opening). As the sash is lowered, the bypass area becomes exposed, effectively increasing
the face opening and dampening face velocity fluctuations thus allowing a nearly constant
total extract rate irrespective of sash position. Because variations in face velocity still occur, it
remains important to utilise the optimum sash height as indicated on the fume cupboard
frame.
3.3.2 Variable Air Volume Fume Cupboards
Variable air volume (VAV) fume cupboards modulate airflow based on sash height by sensors that
detect changes in air pressure or sash position. Sash height is continuously monitored and the
exhaust volume adjusted so that the average face velocity is maintained within acceptable
parameters. VAV fume cupboards are often equipped with a monitor that indicates whether the
cupboard is in ‘standard operation’ or ‘standby operation’ mode. The monitor also has an ‘emergency
purge’ button which increases airflow through the cupboard to maximum and can be used to quickly
remove contaminants (see Figure 2).
Figure 2: Typical monitor and emergency purge control
VAV fume cupboards require technically proficient design, installation and maintenance. The primary
characteristic of VAV fume cupboards is their ability to maintain a constant face velocity as sash height
changes.
33.3.3 Recirculatory Fume Cupboards
In the University recirculatory fume cupboards are not recommended
for working with toxic or flammable vapours or gases.
Recirculating fume cupboards rely absolutely on the absorption of the hazardous vapour or gas by a
filter media, usually carbon, before discharging the ‘cleaned air’ back into the room. If the filter media
becomes saturated, as it will over time, or fails in anyway the hazardous material will enter the room.
The preferred option is always to vent fume cupboards to a safe place outside.
In the event that following a risk assessment a recirculating fume cupboard is the only reasonably
practical option to control a hazardous substance, then clearly the filter must be appropriate for the
chemical you are using at the known or anticipated concentration, always consult the manufacturer.
Because recirculating fume cupboards fail to ‘danger’ they must not be used where failure would
result in exposing users to an immediate threat to life or health. When used they must always be
on a rigorous 6 monthly maintenance contract and be kept under constant review.
3.3.4 High Efficiency Particulate Air (HEPA) Filtered Cabinets
High Efficiency Particulate Air (HEPA) Filtered Cabinets remove particulate material, but NOT gases
or vapours, by passing air through a HEPA filter before discharge to a safe place outside or back into
the room (recirculatory). It must be emphasised that whilst a HEPA filter is an extremely efficient way
of removing solid particles as low as 2 nm in diameter they are not in themselves absorbent and do
not remove hazardous or malodorous gases or vapours. If hazardous vapours or gases are used /
generated in a HEPA filtered cabinet it must be vented to a safe place outside, as with any other fume
cupboard. In addition if a HEPA filtered cabinet were to be considered for both capturing particulates
and handling hazardous vapours and fumes it must be first established that the vapours and fumes
would not have a deleterious effect on the HEPA filter itself or its seals.
Therefore recirculatory HEPA filtered cabinets, have a role in the control of small quantities of toxic
powders during weighing and other non-energetic activities (for further guidance with respect to the
use of HEPA filtered cabinets with powders see the University’s nano-particle safety guidance HSD
147C and HSD 060C on the Occupational Health and Safety Service website
http://www.admin.cam.ac.uk/offices/safety/).
Double HEPA filter cabinets can have the advantage of increased efficiency and a means of changing
filters whilst maintaining containment.
Remember that running a HEPA filtered cabinet when not actually in use and/or storing volatile
chemicals in it may shorten the operating life of the filter as it will slowly become blocked by
background ‘room dust’ in the air and could be damaged by exposure to hazardous vapours.
3.3.5 Microbiological Safety Cabinets / Laminar Flow Fume Cupboards
Although similar in appearance to fume cupboards, they have very different uses. Fume cupboards
should never be used for containment of biological agents. Conversely, the majority of microbiological
safety cabinets (Class 1, 2 and 3) are not suitable for handling hazardous chemicals or gases,
although some are designed and installed for use with both biologically and chemically hazardous
material.
Horizontal or vertical laminar flow cabinets (also called clean benches) are for specimen/sample
preparation only and should never be used for handling either biologically or chemically hazardous
material. The direction of airflow could blow these into the operators face. Laminar flow cabinets
protect the sample NOT the user.
4 SAFE USE OF FUME CUPBOARDS
4.1 The Purpose of a Fume Cupboard
Fume cupboards are typically used to prevent or control exposure to hazardous chemicals. However,
no type of fume cupboard provides total protection and even under ideal conditions some leakage will
occur even with a closed sash. If exposure via leakage poses a significant health risk eg when working
4with substances with very low occupational exposure limits (OEL) - aka workplace exposure limits
(WEL), or very high acute or chronic toxicity (eg toxins or carcinogens) then the use of total enclosure
devices such as glove boxes or isolators should be employed rather than fume cupboards.
Fume cupboards are typically used to:
prevent or control exposure of laboratory workers to airborne substances hazardous to health
and radioactive materials through the capture, dilution and retention of gases, vapours and
(non-infectious) aerosols released within the working chamber or enclosure so they do not
escape into the laboratory
dilute and discharge or otherwise remove hazardous substances so that air released to the
general environment presents no significant human or environmental risk
dilute flammable gases, vapours or dusts in sufficient air to prevent or minimise the risk of
explosion
provide physical protection against spills, splashes and minor fires and explosions
isolate or segregate work activities for reasons of safety, product protection or cleanliness
provide secondary containment in the event of failure of the containing vessels or apparatus
and so limit the potential spread of spills of hazardous materials
Fume cupboards must NOT be used:
for work with biological materials
for the disposal of chemicals
to release especially hazardous chemicals into the atmosphere
to capture contaminants generated elsewhere in the laboratory
as a store cupboard for equipment, unwashed apparatus, malodorous chemicals or chemical
waste and residues
to house large items of equipment, whose bulk can cause major air disturbances within the
fume cupboard body and so compromise the level of containment
4.2 Risk Assessment
Prior to any new experiment or other work being undertaken within a fume cupboard, it will be
necessary to assess the potential hazard posed by the intended procedure. This must be considered
as part of a risk assessment, but will include elements additional to chemical or biological safety. The
risk assessment will identify the hazards (ie substances or conditions with the potential to cause
harm) and evaluate the associated risks (ie the likelihood of that harm being realised). The
assessment must consider conditions other than the normal operating ones, ie spillage, catastrophic
failure of any component within the system (ie fan), or any other condition likely to present adverse
conditions eg loss of electrical power. The assessment must define the controls that are to be in place
and ensure that they are suitable and sufficient eg laboratory rules, lone working, personal protective
equipment (PPE), written procedures, the use of spill trays/secondary containment, inspection regime,
maintenance, cleaning, work organisation, airflow performance, competence of those undertaking the
work, and level of supervision.
4.3 How to Use a Fume Cupboard
The degree of protection to a hazardous substance offered by a fume cupboard can be rapidly
reduced if the following advice is not followed. It should be noted that no fume cupboard, however well
designed, can provide adequate containment unless good laboratory practices are used. Adequate
planning and preparation are key. It is important that the fume cupboard limitations are recognised.
It may be necessary to use special containment devices such as glove boxes or specialised fume
cupboards for perchloric acid or hydrofluoric acid.
Prior to use confirm that the fume cupboard is suitable for the purpose and is operating
satisfactory, ie check the on/off controls, operation of sash, audible or visible sash height
alarm (where fitted) and light operation
Check the airflow gauge/indicator to see whether the fume cupboard is operating above its
minimum rate of airflow. In the absence of an airflow indicator, it maybe necessary to feel air
movement into the cabinet or to check the face velocity. A Fume Cupboard Pre-Use Operator
Checklist could be utilised. An example is included in Appendix 1.
NB. The fact that a fume cupboard is switched on does not confirm that air is flowing
through the system and at the required airflow
5 If the fume cupboard is not working correctly report the fault to your Departmental Safety
Officer or Maintenance Section (where applicable)
Ensure that the floor area in front of the fume cupboard is unobstructed with furniture or
equipment and close any windows or doors which may interfere with the performance of the
fume cupboard (air currents and turbulence in the room caused by doors, windows, walls, and
furniture and other obstructions placed too close to the fume cupboard could affect its
performance and containment efficiency)
Do not position fans or air conditioners in the room in a manner that will direct airflow across
the face of the fume cupboard as this could affect the containment of the cupboard
Ensure sufficient room inside the fume cupboard to do what is required. Remove unwanted
apparatus and equipment and avoid all unnecessary clutter
Where practicable, place everything needed inside the fume cupboard before starting a
procedure (this should reduce the number of arm movements into and out of the working
aperture, a major cause of fume escape)
Maintain the protective air barrier for a safe work area by ensuring that a 150 mm wide
‘equipment free zone’ is maintained behind the sash at all times
Figure 3: Formation of protective air barrier
When standing directly in front of a fume cupboard, an area of low pressure is formed in front
of the user by the air passing their body to enter the cupboard. This zone of low air pressure
extends into the fume cupboard for approximately 100 mm. Hazardous substances may be
drawn out of the cupboard and may enter this turbulent area, which is directly in the breathing
zone (see Figures 3 & 4). Convection currents caused by movement outside the cupboard
enclosure and eddy currents caused by the placement of objects in the zone of low pressure
may also lead to hazardous substances being drawn out of the fume cupboard
Bad placement of Good placement of Best placement of
materials materials materials
Figure 4: Placement of materials within fume cupboards
Avoid using large objects inside the cupboard as these may have an adverse effect on
performance and block the rear slots (see Figure 5). If large equipment must be placed inside
the fume cupboard, it should be raised approximately 50 mm to allow air to pass beneath the
object and placed near the rear of the cupboard taking care not to block the rear slots
6Poor placement of large Good placement of large
equipment equipment
Figure 5: Placement of large objects / equipment within fume cupboards
Arrange apparatus within the cupboard to allow the operator normal access with the sash in
as low a position as possible; and not greater than 0.5 m, and do not position equipment so far
back that it obstructs the rear slots
Know the health hazards of the materials you are working with and become familiar with the
signs and symptoms of overexposure
Keep the sash lowered whilst an experiment is in progress and the fume cupboard is
unattended. Fume cupboards with horizontal sliding panes should be used with the sash all
the way down, with as small an open area as possible
Where there is the potential for explosion additional shielding must be used
Do not put your head inside the fume cupboard enclosure at any time whilst hazardous
substances are present
Avoid sitting at the cupboard as this may result in a ‘lap full’ of chemicals and it restricts
mobility in an emergency
Proper use of a fume cupboard does not negate the need for proper Personal Protective
Equipment (PPE). Use suitable PPE (lab coats, gloves, goggles or face shields) at all times
when working at a fume cupboard
Where possible, chemicals must not be stored in the fume cupboard and where they are,
quantities must be kept to a minimum ie those in current use
All chemicals placed inside a fume cupboard must be clearly labelled
Do not leave equipment such as hotplates or stands in a fume cupboard if they are not part of
the current experiment
Ensure lightweight items such as tissues, disposable gloves and filter papers are not allowed
to be drawn into the fan blades as they can degrade extract performance
When highly hazardous substances are being used eg carcinogens, the fume cupboard
should be appropriately labelled (an example is given in Appendix 2)
Exercise extreme caution with ignition sources inside a fume cupboard. Ignition sources such
as electrical connections, variac controllers and naked flames should only be used inside the
cupboard if there are no operations involving flammable or explosive vapours. If possible,
ignition sources should remain outside the fume cupboard
All electrical devices should be connected outside the fume cupboard to avoid electrical arcing
that can ignite a flammable or reactive chemical
Avoid sources of high heat load within the fume cupboard as these will disturb the airflow
pattern and reduce the overall efficiency of containment
7 Clean all spillages promptly and all chemical residues from the fume cupboard enclosure after
each use and keep the sash clear at all times
Plan for possible emergencies. Fires in fume cupboards should be approached with extreme
caution. The use of high pressure CO2 extinguishers can result in flames being blown into the
duct work.
4.4 Fume Cupboard Limitations
Used appropriately, a fume cupboard is a very effective device for the containment of hazardous
materials, as well as providing some protection from splashes and minor explosions. However, the
average fume cupboard does have some limitations. Examples are given below:
Airfoil sills: The majority of fume cupboards are equipped with flat or rounded sills or airfoils
which direct flow or air smoothly across the work surface. Sills should not be removed or
modified by the user. Objects should never be placed on these sills. Materials released
from containers placed on the sills may not be adequately captured. In addition, an object
placed on the sill may prevent the quick and complete closure of the sash in an emergency
Explosions: A fume cupboard is not capable of containing an explosion even when the sash
is fully closed. If an explosion hazard exists, the user should provide anchored barriers,
shields or enclosures of sufficient strength to deflect or contain it. Such barriers can
significantly affect airflow in the fume cupboard
Horizontal sliding sashes: These should never be removed. Horizontal sash fume
cupboards are designed and balanced with no more than half the face open at any time.
Removal of the sashes may reduce the face velocity to below acceptable levels
Hydrofluoric acid: A conventional fume cupboard should not be used for large quantities of
concentrated hydrofluoric acid. Where the work undertaken predominantly uses concentrated
hydrofluoric acid, an appropriately rated dedicated fume cupboard equipped with a
polypropylene work surface, a wash down system and transparent PVC sash should be used
Particulates: A fume cupboard is not designed to contain high velocity releases of particulate
contaminants unless the sash is fully closed
Perchloric acid: A conventional fume cupboard must not be used for heating perchloric acid.
Perchloric acid vapours can settle on ductwork, resulting in the deposition of perchlorate
crystals. Perchlorates have been known to detonate on contact, impact or friction causing
serious injury to researchers and maintenance personnel. Specialised perchloric acid fume
cupboards equipped with a wash down system must be used for such work
Pollution control: An unfiltered fume cupboard is not a pollution control device. All
contaminants that are removed by the ventilating system are released directly into the
atmosphere. Apparatus used in fume cupboards should be fitted with condensers, traps or
scrubbers to contain and collect waste solvents or toxic vapours and dusts
Pressurised systems: Gases or vapours escaping from pressurised systems may move at
sufficient velocity to escape the fume cupboard
Tubing for exhaust: Tubing is frequently used to channel exhaust to the fume cupboard from
equipment located outside the fume cupboard enclosure. This is not an effective control
measure
Waste disposal: A fume cupboard should not be used for waste disposal.
4.5 The Fume Cupboard as a Storage Device
Fume cupboards are designed specifically to provide ventilation for the protection of lab occupants
during chemical manipulations. The airflow they provide is greatly in excess of that needed for storage
of closed containers of even the most toxic of materials.
In general, the storage of chemicals within fume cupboards is strongly discouraged, unless it is for the
reaction at hand. However, the realities of available space and equipment within laboratories within the
University may make it difficult or completely impossible to prohibit the use of fume cupboard for
storage. Where this is the case, the following is recommended:
4.5.1 Fume Cupboards Actively in Use for Experimentation
Storage of materials should be minimised or eliminated where possible as materials stored in the fume
cupboard can adversely affect the containment provided. Each item placed on the work surface
interferes with the directional airflow, causing turbulence and eddy currents that allow contaminants to
8be drawn out of the enclosure. Even with highly volatile materials, as long as a container is properly
capped evaporation will not add significantly to worker exposures. It should be noted that as the fume
cupboard is the focus of the most hazardous activities conducted within a laboratory, the presence of
flammable or volatile, highly toxic materials can exacerbate the problems resulting from an explosion
or fire within the enclosure. Even if they are not directly involved, attempts to control or extinguish a
fire may result in the spilling of stored material. Unlike a fume cupboard, flammable materials storage
cabinets provide additional protection in the event of a fire.
4.5.2 Fume Cupboards not in Active Use
Materials requiring ventilated storage (eg flammable and highly toxic, or malodorous substances) may
be stored in a fume cupboard if they are properly segregated and the fume cupboard is labelled to
prohibit its use for experimental work.
4.6 Shared Use of Fume Cupboards
Where two or more users share the same fume cupboard it is important, and a legal obligation, that
they cooperate and communicate in order to ensure that their experiments are compatible and do not
introduce any additional hazards in the event of a reasonably foreseeable accident / incident.
4.7 Common Fume Cupboard Myths
Myth - When working with highly dangerous materials, the higher the face velocity the better.
-1
Whilst it is important to have a face velocity between 0.4 – 0.6 ms , velocities higher than this are
-1
actually harmful. When face velocity exceeds 0.6 ms eddy currents are created which allow
contaminants to be drawn out of the hood, increasing worker exposures.
Myth - The airfoil on the front of a fume cupboard is of minor importance. It can safely be removed if it
interferes with my experimental apparatus.
Airfoils are critical to efficient operation of a fume cupboard. With the sash open an airfoil smoothes
flow over the enclosure edges. Without an airfoil eddy currents form, causing contaminates to be
drawn out of the fume cupboard. With the sash closed, the opening beneath the bottom airfoil provides
for a source of exhaust air.
Myth – Using a fume cupboard makes my work safe.
A fume cupboard is only part of your safety systems – remember its limitations, and appreciate that
protection is being afforded mainly by nothing more than airflow which can be relatively easily
disturbed.
5 TESTING AND MAINTENANCE
A fume cupboard system will require regular examination, testing and maintenance to ensure
continued safe operation. The maintenance requirement applies to the whole system, from fume
cupboard to discharge stack. A planned preventative maintenance schedule must be established for
each fume cupboard prior to commencing use. This will place responsibility on users, departments and
EMBS. Reference should be made to the Service Level Agreement to determine departmental and
EMBS responsibility.
5.1 Frequency of Maintenance
The COSHH Regulations require control measures used to prevent exposure to hazardous
substances to be maintained in an efficient state, in efficient working order and in good repair. In
addition thorough examination and tests must be carried out at least once every fourteen months. In
practice this frequency of testing may be increased in accordance with the risk assessment of the
effects of system failure. The schedule recommended in this guidance includes elements at both six
and twelve monthly intervals (refer to Appendix 3). Where system failure would result in significantly
high risk of exposure it may be appropriate to halve the indicated intervals, or supplement them with
additional checks and measures. These examinations are additional to the pre-use operator checks.
Additional checks to those listed in Appendix 3 might include:
Checking filters for saturation and replace if necessary (if fitted)
If fitted, check the operation of water wash down/fume scrubber
9 Check the make-up air heating controls and its temperature
Remove the baffle, if fitted, and clean both the baffle and the rear of the chamber
5.2 Responsibilities
Departments, Estate Management and Contractors all have specific responsibilities for the testing
and maintenance of fume cupboards. Systems should be in operation within a department to
ensure air flow face velocities are tested regularly and signed records kept for a minimum period of
5 years from date of last entry (see Section 6), that Estate Management (Services Maintenance
Unit) and/or an external maintenance contractor are contacted in the event of breakdown, that
fume cupboards are decontaminated prior to any maintenance work being undertaken and that
‘permits-to-work’ are issued and completed prior to any maintenance work being undertaken.
Permits-to-work should identify what measures must be taken to reduce the risks or make the area
safe, what risks remain and what steps must be taken to avoid harm.
Written records of maintenance work must also be kept for a minimum of 5 years including details
of all repaired and replaced components. These records should be signed and dated by those
responsible for the work.
Due to the fact that maintenance activities will present those undertaking them with hazards other
than those present during normal fume cupboard operations, EMBS and departmental staff must
ensure that adequate precautions are taken to protect the health and safety of personnel engaged
in the examination, testing, maintenance and repair of fume cupboards and others that may be
affected by these procedures. This can be achieved by:
Instruction and training on recognition of hazards and assessment of risks from those
hazards. There will be hazards associated with the maintenance itself (namely electricity,
unguarded mechanical parts, hand tools, manual handling, access at height – from ladders
and platforms) as well as those created by activities performed within the fume cupboard
(namely chemicals and dust, biological agents and radioactive substances)
Undertaking a risk assessment for the maintenance work prior to any maintenance work
being carried out
Devising safe systems of work which incorporate appropriate controls including
competence, training, personal protective equipment and supervision. This might include
implementing a permit-to-work system
Informing others that work is being carried out
Devising procedures to avoid contamination
Consideration of disposal of parts etc (eg contaminated ductwork) before work commences
Avoiding triggering fire alarms eg with smoke tracers
It may also be necessary to neutralise and decontaminate fume cupboards prior to the
commencement of any maintenance work. Users are responsible for decontaminating fume
cupboards. However, due to chemical contamination of fume cupboard duct systems any repair
work on these installations must be progressed via Estate Management and through a ‘permit-to-
work’ system.
Where maintenance work is undertaken on roofs near to fume cupboard discharge ducts, the
Departmental Safety Officer and/or Chief Maintenance Engineer within a department must be
contacted prior to the commencement of work in order to have the extract system stopped and/or
made safe whilst the work is in progress. Due to the disruptive nature of turning off the extract
system, where possible prior notice of at least 24 hours will be required and working methods must
be agreed in advance.
In addition, if work on roof tops is needed to check fume cupboard ducting and plant, consideration
must be given to the weather conditions. High winds, rain, snow and ice can all considerably
increase the risks to those involved in the maintenance. A decision must be made by the person
supervising the work as to whether the work is continued.
106 FUME CUPBOARD PERFORMANCE TESTING
Performance testing is essential to confirm that the fume cupboard is operating to a level to provide
the desired fume arrest, containment and removal. It is appropriate in the following situations:
1) Part of the commissioning of new installations
2) Part of regular thorough examination and testing to comply with COSHH Regulations
3) Following maintenance activities
6.1 Frequency of Testing
The COSHH Regulations require employers to conduct thorough examination and test of engineering
control measures at least once every 14 months. In some instances more frequent tests will be
necessary. This must be determined by a risk assessment.
6.2 Record Keeping
The COSHH Regulations require suitable records of test results to be maintained for at least 5 years
from the date of the last test. Appendix 4 provides an example Record Sheet.
6.3 Test Principles
6.3.1 Flow Visualisation Test
This test is a non-quantitative assessment of airflow characteristics, to examine ability of the fume
cupboard to contain and remove substances.
A smoke test can be conducted by the use of a smoke pellet or a smoke-tube. The technique is to
ignite a smoke pellet placed in a suitable container within the fume cupboard and note the behaviour
of the smoke to assess the turbulence, clearing the base of the fume cupboard, and the efficiency of
general contaminant removal without dead spots. The same observations can be made by using the
smoke tubes which allow controlled release of ‘puffs’ of smoke into particular zones of the fume
cupboard. The observations should be recorded and where necessary alterations within the fume
cupboard can be made to improve performance. Alternatively a hand-held smoke generator (often
referred to as a ‘cumulus’) can be used.
6.3.2 Face Velocity Test
This test determines the airflow (face velocity) across the sash opening. Face Velocity is measured
over grid points of the maximum working aperture and a mean velocity calculated for each grid point.
The mean of these area values is reported as the average face velocity. Refer to Appendix 5 for the
test procedure.
The test will not demonstrate containment performance, but is a valid measure of the mechanical
performance of the fume cupboard. It is a quick and easy check that can be applied during an initial
fault finding exercise.
Acceptance Criteria*
Face Velocity
-1
-1 Optimal 0.5 ms at
Recommended Range 0.5-0.8 ms
0.5 m sash height
-1
Maximum acceptable velocity 1.0 ms
-1
Minimum acceptable velocity* 0.3 ms
Maximum deviation from mean velocity
value of any other measurement within the +/- 15%
grid
11* It should be noted that in some laboratories low face velocity fume cupboards have been installed
-1
which are designed to provide safe containment at a mean air velocity of 0.25 ms . These fume
cupboards should be labelled to this effect.
Factors to consider when assessing face velocity results
The range of acceptable values is open to debate. However, the following are generally accepted
principles:
-1
i) Face Velocity too fast. Velocities greater than 0.8 ms are likely to generate eddy currents
around users standing in front of the cupboard and these are then able to draw contaminants
out through the aperture, particularly during movement by the operator
-1
ii) Face velocity too slow. It is unlikely that velocities below 0.4 ms are able to arrest and
contain contaminants within the enclosure, particularly where external air movements due to
movement of users or opening/closing of doors and windows are likely to exceed the face
velocity unless the fume cupboard is designed specifically to operate at low face velocities
Where fume cupboards are found to have face velocities, which lie outside the recommended or
acceptable values, steps must be taken to modify the system.
Subsequent testing should assess the effect on the performance of the system as a result of
adjustments to the air flow rate.
6.3.3 Containment Test
The most accurate way of judging performance of fume cupboards is by assessing the ‘containment’.
However, the test takes a long time and requires special equipment. The containment test is usually
performed at design stage for commissioning a fume cupboard.
The test consists of releasing a material at a known rate inside the fume cupboard and measuring the
presence of material just outside the sash.
There are situations when it is advisable to carry out a containment test on an installed fume
cupboard. For example when smoke tests have suggested turbulent air movement within a cupboard
(despite the average face velocity being acceptable) and instances of complaints of unpleasant smells
emanating from a fume cupboard (despite the satisfactory face velocity measurements). In these
instances a containment test is warranted.
A number of methods have been suggested to determine the efficiency with which a fume cupboard
‘contains’ a contaminant, or prevents escape of contaminant out through the sash opening. They all
consist of releasing a material at a known rate inside the fume cupboard and measuring the presence
of material just outside the sash opening.
12References and Further Reading
British Standards Institution
BS 7258: 1994: Laboratory Fume Cupboards (BS 7258: 1994 now largely superseded)
Part 1: Specifications for safety and performance
Part 2: Recommendations for the exchange of information and recommendations for installation
Part 3: Recommendations for selection, use and maintenance
Part 4: Method for determination of the containment value of a laboratory fume cupboard.
BS EN 14175: 2003-2006: Fume Cupboards
Part 1: Vocabulary
Part 2: Safety and Performance Requirements
Part 3: Type Test Methods
Part 4: On-site Test Methods
Part 5: Recommendations for Installation and Maintenance (in preparation, draft available)
Part 6: Variable Air Volume Fume Cupboards
BS 7989: 2001: Specification for Recirculatory Filtration Fume Cupboards
BS 5726: 2005. Microbiological Safety Cabinets (BS 5726: 1992 now largely superseded)
Part 2: Recommendations for information to be exchanged between purchaser, vendor and installer
and recommendations for installation
Part 4: Recommendations for selection, use and maintenance
BS EN 12469: 2000: Biotechnology Performance Criteria for Microbiological Safety Cabinets
EN 13150: 2001: Workbenches for laboratories – Dimensions, Safety Requirements and Test
Methods
Health and Safety Executive
The maintenance, examination and testing of local exhaust ventilation, HS(G)54 Second Edition;
1998; HSE Books
Control of substances hazardous to health. The Control of Substances Hazardous to Health
Regulations 2002. ACOP and Guidance L5 2002
University
EMBS (SEPT 1998); Engineering Services Design Guide and Consultants Brief for University
Buildings
EMBS (2003); Design Guide and Consultants Brief for University Services and Construction Works.
13Appendix 1 - Fume Cupboard Pre-Use Operator Checklist
FUME CUPBOARD PRE-USE OPERATOR CHECKLIST
(Tick to Confirm)
To be completed EACH day that the fume cupboard is used
Fume Cupboard No: Location:
Date On/Off Sash Flow Internal Fault Conditions Signed
Indicator Light
14Appendix 2 - Fume Cupboard Label
Maintenance staff or others not directly connected with the experiments may need to know what
substances are being released into the system. The following label can be used to record hazardous
substances being used within a fume cupboard, contact name and internal phone number. This
information can supplement the information contained on an ‘out of hours’ or ‘overnight’ card.
FUME CUPBOARD CONTENTS
FC No. Group:
Hazardous substances used (eg carcinogens):
Contact details Name:
Phone:
Important!
1. Keep this information up-dated.
2. Report all breakdowns immediately.
15Appendix 3 - Fume Cupboard Maintenance Schedule
Interval between
Maintenance
Fume Cupboard Maintenance Schedule 6 Months 12 – 14
Months
Enclosure
Visual examination to ensure integrity of enclosure, including seals around main
panels, sinks and other services. Check storage voids underneath main aperture. *
Check operation of enclosure light.
*
Replace enclosure light (ie fluorescent tube).
*
Controls
Activate on/off switch to confirm operation, and note operation associated warning
lights.
*
Operate any other warning devices (ie sash height or low-flow switches) to confirm
operation.
*
Check air-flow indicator device. In case of liquid manometer disconnect tubing and
re-zero, then switch on fume cupboard and note movement of fluid column. *
Sash
Repeat movement of the sash through its entire travel to confirm ease of operation
(lubricate where necessary). *
Check operation of working aperture stop and over-ride mechanism.
*
Check alignment of pulleys and condition of pulley wires (replace distorted or broken
wire).
*
Inspect sash screen for cracks, chemical attack, or any other damage likely to
adversely affect transparency of the screen. *
Ducting
Examine fume cupboard-to-ductwork connection to confirm seal and physical
condition.
*
Conduct visual examination of entire ductwork run for mechanical damage and leaks,
including internal sections where condensate or any other concentrations are likely *
to cause damage.
Inspect mechanical volume flow control dampers to confirm freedom of movement,
and absence of internal obstruction. *
Examine fire dampers for corrosion, and operate where possible.
*
Examine flow-sensing devices, or any other equipment located within the ductwork
and replace if damaged. *
Fan
Check flexible coupling (including tie-clips) to ductwork for damage, wear or leakage.
*
Visual examination of anti-vibration mountings.
*
Visual examination of all external features for mechanical integrity.
*
Visual examination of inside the fan casing to confirm physical integrity, absence from
obstructions (ie tissues, rubber gloves, filter papers). *
Examine electrical supply cables, switch-gear, connectors and isolators for physical
damage and continued electrical operation. *
Check rigidity of exhaust stack
*
Check condition and tension of drive belt, re-tighten or replace if necessary
*
Fit new drive belt.
*
Check drive-shaft bearings for excess movement or other signs of wear.
*
Re-grease bearings.
*
Lubricate electrical motor in accordance with manufacturer’s recommendations.
*
16Appendix 4 - Record of Examination and Test of Laboratory Fume Cupboard
1. Equipment and Location
FC Number: ………………………………………………………. Site: ………………………………
Type: ……………………………………………………………….. Building: …………………………
Manufacturer: …………………………………………………….. Room: ……………………………
Date of last examination and test: ………………………………
Date of test: ……………………………………………………….
Name of tester: ……………………………………………………
Tester’s signature: ………………………………………………..
2. Process under control Hazardous substances present
1. …………………………………………………. 1. ……………………………………………….
2. …………………………………………………. 2. ……………………………………………….
3. …………………………………………………. 3. ……………………………………………….
4. …………………………………………………. 4. ……………………………………………….
3. Conditions at time of test in service indicate contents at time of test
stood down ……………………………………………..
other ……………………………………………..
4. Permit-to-work completed and controls in place
5. Examination and test details Pass Fail N/A Comments
a) Controls i) Fan on/off ……………………..
ii) Enclosure light ……………………..
b) Flow indicators i) Fluid manometer ……………………..
ii) Electro. Mech. ……………………...
Light
Audible warning
c) Enclosure i) Sash operation ……………………...
ii) Sash height limiter ……………………...
iii) Sash height warning ……………………...
Light
Audible warning
iv) Sash transparency ……………………...
176. Face velocity measurements
2
Aperture width …………… mm Aperture area …………… m
Sash opening Height (max) …………… mm
Height (test) …………… mm
Speed setting (where applicable) High
Low
Anemometer Vane Date of calibration ……………………
Thermal
-1
Face velocity at commissioning ……………………………ms
Grid Position
1 2 3 4
Reading No.
Row A
(time interval)
1 (15 s)
2 (30 s)
3 (45 s)
Mean
Corrected Mean
Row B
1 (15 s)
2 (30 s)
3 (45 s)
Mean
Corrected Mean
Row C
1 (15 s)
2 (30 s)
3 (45 s)
Mean
Corrected Mean
-1
Grand Mean ms
(± 15%) to
18Appendix 5 - Face Velocity Test
Although it is established that face velocity measurement will not demonstrate containment
performance, the face velocity is still a valid measure of the mechanical performance of the system,
and is also a quick and convenient check that can be applied during an initial fault finding exercise.
Measurements of face velocity are made in the plane of the sash opening (face), in the direction at 90°
to the plane of the sash. Measurements are taken at a number of grid points evenly distributed
throughout the face, giving three rows of measurements (the number of measurements in each row is
determined by the width of the face). A mean velocity is calculated for each grid point. The mean of
these area values is reported as the average face velocity.
1. Apparatus
a) Anemometer - with vane diameter not less than 60 mm and not exceeding 100 mm, calibrated
by an accredited test laboratory
b) Support system – a laboratory retort stand and clamp or similar device to hold the
anemometer vane head at the prescribed positions in the plane of the sash opening. The
chosen system should cause the minimum obstruction to airflow
c) Stopwatch
d) Tape – if necessary
2. Test Conditions
a) The fume cupboard under test must be empty of equipment and clean.
b) Doors, windows and other similar openings must remain closed throughout the test. The
make-up air supply, if fitted, must be operating normally. Switch on any other extraction
systems in the room. All other fume cupboards in the room must also have their sash set at its
maximum working aperture (500 mm).
3. Determination of the points of measurement (see Figure 6)
a) Define a rectangle such that the sides of the rectangle are 75 mm from the edges of the
working aperture
b) Divide the height of the rectangle by 2 to give effectively 3 rows (row A, row B and row C)
c) Divide the width of the rectangle by a whole number n, such that the width of the cells formed
does not exceed 350 mm
d) The corner of the cells define 3(n+1) grid positions at which the anemometer is held or fixed
4. Method
The procedure to measure face velocity across the sash opening is carried out as follows:
a) Set the sash at the sash stop. If there is no sash stop set the sash at 500 mm. It may be
necessary to have a lower sash opening to achieve the necessary face velocity of 0.5m/sec. If
so the sash and jamb must be clearly marked to show the maximum height at which this
velocity can be achieved
b) Either by eye or tape divide the sash opening of the cabinet into equal rectangular areas: The
grid should begin 75 mm from each edge. Divide the area into two halves (top and bottom)
and then divide with vertical lines to form a grid such that the width of each zone does not
exceed 350 mm (see Figure 6)
c) Position the anemometer head at the corners of each of the rectangles (NB. ensure that no
part of the vane head support system lies in the airflow through the vane head and that all
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