Optical Radiation Transmission Levels Through Transparent Welding Curtains
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Optical Radiation Transmission Levels
Through Transparent W e l d i n g Curtains
Tests with blue, green, gray and yellow welding curtains
from commercial sources indicate yellow curtains transmit a larger
component of hazardous wavelengths than the others,
although the magnitude of optical energy
transmitted by yellow curtains is small
BY C. EUGENE MOSS
ABSTRACT. Results are described for communication among workers and poraled, and Wilson Sales Company.
tests conducted on 25 transparent with management. Industrial use of As far as it can be determined these
welding curtain samples of four colors the transparent curtains, however, has were the only k n o w n manufacturers of
from five manufacturers to document resulted in questions concerning the transparent welding curtains at the
spectral transmission values of curtains protection they afford workers and time of testing.
used in welding environments. The observers outside the immediate Some samples had been previously
conclusion based on the results of welding area. However, the published acquired which enabled transmission
these tests suggests that most transpar- literature, excluding manufacturers' tests to be conducted on aged
ent curtains will afford adequate specifications, for such curtains is curtains. In addition, a used bicolored
protection from optical radiation in limited." For this reason the National welding curtain was obtained from an
the ultraviolet region, but that all of Institute for Occupational Safety and industrial welding facility. Samples
them will transmit high percentages of Health undertook tests to determine from this particular curtain permitted
infrared radiation. optical radiation protection provided spectral transmission comparisons to
by transparent welding curtains: this be made on a before and after clean-
Introduction paper describes the results of the tests ing condition.
performed. Table I categorizes the samples
Numerous skin and eye injuries have tested according to manufacturer, col-
occurred in the welding environment or, thickness, and age.
Apparatus and M e t h o d s
from exposure to ultraviolet, visible,
and infrared radiation (hereinafter de- Acquisition of Welding Curtain Samples Transmission Measurement System
noted optical radiation). 1 7 A control
measure that has been used to reduce Samples of transparent welding cur- All spectral transmission measure-
the incidence of injuries to bystanders tains were requested from all those ments were performed w i t h a Perkin-
consists of using welding curtains manufacturers w h o were identified Elmer Model 323 recording spectro-
made of metal or flame-resistant fabric through a search of the welding trade photometer. This system has a low
that are generally opaque to most o p t i - literature. Twenty-one curtain samples sensitivity level which makes it a valu-
cal radiations. of various colors and sizes were able tool to document low transmis-
received. sion values. The spectrophotometer is
A relatively recent innovation in
Manufacturers that provided sam- a double-beam single-pass recording
curtain material has been the use of
ples were Davlynne Incorporated, FIRL monochromator that uses deuterium
transparent colored curtains made
Industries Incorporated, Frommelt In- and tungsten lamps as the optical radi-
from polyvinyl chloride plastic film
dustries, Singer Safety Products Incor- ation sources. The detector used in the
and at least three other components.
These components are a color dye, system consists of a photomultiplier
flame retardant chemical, and an tube for the ultraviolet and visible
Paper to be presented at a symposium
ultraviolet absorber. The intensity and regions, and a lead-sulfide cell for the
sponsored by the AWS Safety and Health
spectral distribution of transmitted Committee during the AWS 60th Annual infrared region. The spectral range of
optical radiation through a given Meeting in Detroit, Michigan, April 2-6, the spectrophotometer was 210 to
curtain depends, in some manner, on 1979. 2600 nanometers (nm), i.e., 8.3 x 1 0 "
such factors as optical density, thick- to 102.4 x 10 " in.*
C EUGENE MOSS is a Health Physicist, U.S.
ness, and color.
Public Health Service, National Institute for
One of the main advantages of using Occupational Safety and Health, Cincin- *7 nanometer (nm) = I Xo 70 " m = 39.4 X
such curtains is the increased visual nati, Ohio. 10 " in. = 70 angstroms (A).
W E L D I N G RESEARCH S U P P L E M E N T I 69-s
does not vary too much, since the
Table 1-Data on Tested Curtain Samples intensity of transmitted radiation is
dependent on thickness. To check
Thickness""" 1
how well the manufacturer controlled
Sample Color cm ,ge in years
the thickness of the curtains, transmis-
A Yellow 0.0351 > 1 sion measurements were compared
B Green 0.0356 > 1 among samples cut from separate
C Gray 0.0328 > 1 sheets of the same curtain type. As part
D Yellow 0.0361 > 1 of this test a measurement was made
E Green 0.0328 > 1
to obtain the thickness of each sample
F Yellow 0.0335 > 1
G w i t h a micrometer. The average thick-
Yellow 0.0368 < 1
H Green 0.0312 < 1 ness is shown in Table 1.
Gray 0.0297 < 1
Blue 0.0312 < 1 Transformation Technique
K Green 0.0305 < 1
L Yellow 0.0307 < 1 A program was developed for a
M Gray 0.0328 < 1 Hewlett-Packard M o d e l 9830A com-
N Green 0.0307 < 1 puter to transform transmission values
O Yellow 0.0358 < 1 from the three separate optical radia-
P Green 0.0300 < 1 tion regions into one continuous curve
Q Yellow 0.0353 < 1 on semi-logarithmic graph paper. This
R Yellow 0.0310 > 1 format permitted better comparisons
S Blue 0.0297 > 1
among the various samples.
T Yellow 0.0328 < 1
W Gray 0.0371 > 1
X Green 0.0351 < 1 Results
z Yellow 0.0310 > 1
A typical sample spectral transmis-
'•'Thickness given is average of three measurements sion plot as obtained from the spectro-
' " 2 . 5 4 c m = 1 in.
photometer is shown in Fig. 1. Note
After the recommended warm-up letter, placed into an envelope until that the three optical regions were
period, the spectrophotometer was the order of measurement was deter- divided as follows: ultraviolet 210-360
calibrated at the lowest wavelength mined by a random number process, nm, visible 340-700 nm, and infrared
value in each of three optical radiation and measured. Each of the samples 600-2600 nm.
regions at both the zero and 100% was positioned at the entrance slit of The original data, while informative,
transmission level. The instrument was the detector chamber. Care was taken have several disadvantages in their
set for 100% transmission and exam- during the tests to position all samples existing format. First, curves shown in
ined for departure from 100% across over the cell w i n d o w in the exact same this manner are difficult to read w i t h
the entire spectral range of all regions. manner by the use of adhesive tape samples that have unusual transmis-
A zero-check was made at the end of strips. Cloves and tongs were used to sion properties. Second, comparisons
each region to determine the magni- minimize contamination. A plot of w i t h samples having different spectral
tude and direction of any drift correc- percent transmission vs. wavelength transmission values are laborious. Fi-
tions. was made on every sample. nally, the curves do not follow the
A rectangular-shaped segment, ap- standard division of optical radiation
proximately 25 X 50 mm (1 X 2 in.) regions w h i c h are ultraviolet, less than
Reproducibility 400 nm, visible 400-760 nm, and
was cut from the center portion of
every sample, assigned an arbitrary It is important that curtain thickness infrared, greater than 760 nm. These
z
o
CO
s
z
<
z Transmission Range Optical Region
LU 0-7% Ultraviolet (210-360 nm)
U
0-700% Visible (340-700 nm)
0-700% Infrared (600-2600 nm)
NANOMETERS
Fig. 1—Typical spectral transmission curve of welding curtain obtained for ultraviolet radiation is 1% and for visible and infrared
radiation is 100%
70-s|MARCH 1979
IOOO 1300 IOOO 1300 1600 1900 2200
NANOMETERS
NANOMETERS
Fig. 2—Typical modified spectral transmission plot Fig. 3—Composite of green curtains (samples B, E, H, K, N, P
and X)
difficulties can be averted by using the
previous mentioned transformation sion tendency in this area while the during the time of study. Therefore,
format technique. When this format is yellow and blue samples demonstrate one should not assume only aging
used, a composite curve such as in Fig. a very sudden and distinct transmis- caused the effect observed. Note that
2 results. sion change around 500 and 800 nm, w i t h the same curtain, sample trans-
There is a small error in the compos- respectively. mission values appear to decrease as
ite curves due to the difference in 4. All curtain samples transmit in- the contaminant level increases—Fig.
sensitivity of the two sequentially used frared radiation. For example, the blue 10.
spectrophotometer detectors. The er- and yellow samples will transmit A theoretical relationship exists be-
ror associated w i t h this factor is about about 90% in the infrared (IR) region tween spectral transmission levels and
5% and occurs at the junction of the while the gray samples transmit the thickness of the curtains provided that
visible-infrared region. least at 20%. the curtain tint and its concentration
In order to determine the degree of Samples of the same color and are the same. This relationship is
spectral transmission uniformity in the approximately equivalent thickness, shown as equation (1):
manufacturing process, a comparison but differing in age, generally show I (\) = \e(\)e-*«>* (1)
was made among all curtain samples variation of transmission levels over
of the same color. Figures 3-6 show the measured optical radiation region In this equation, which is often
sample data according to color. Sev- of less than 5% (Figs. 6, 7, and 8). referred to as Lambert's Law of
eral characteristics are apparent from However, Fig. 9 suggests that aging Absorption, l„ is the optical radiation
these figures: factors may be quite important for incident upon the welding curtain, I is
1. Except for the yellow curtain yellow curtains in the ultraviolet (UV) the optical radiation transmitted
samples there appears to be relatively region. Figure 9 also shows the older through the curtain, x is the curtain's
good consistency in transmission val- samples permit more transmission thickness, and k is the absorption coef-
ues, i.e., less than 10% variation over near 400 nm. In fact, four of the five ficient.
the measured optical region. The new yellow samples, from different Equation (1) can be rewritten as:
yellow samples appear to give consis- manufacturers, have a high absorption
tent values, except in the UV region. level of around 400-500 n m , whereas
log, -kx (2)
2. All samples experience a drop in none of the older samples show this
characteristic.
(T)
transmission around 1700 nm. This
particular decrease in transmission is Since none of these curtain samples A comparison between t w o curtains
probably due to curtain composition. are older than one year, this particular (A and B), identical except for thick-
3. The shape of the transmission apparent aging effect could be of ness, can be made by taking the ratio R
curve undergoes drastic change be- major importance. It must be noted, of equation (2) for the t w o curtains:
tween the visible and IR regions. For however, that there is no assurance
example, the green and gray samples that sample composition or manufac- R =
show a gradual transmission progres- turing methods had not changed (,)^-(T)
WELDING RESEARCH SUPPLEMENT I 71-s
io V
-
z
o
/ /
- fjt
z
LU
u
\
l l l l l l l
100 400 700 1000 1300 1600 1900
NANOMETERS
Fig. 4—Composite of yellow curtains (samples A, D, F, G, L, O, Q, T Fig. 5—Composite of gray curtains (samples C, L, M and W)
and Z)
7
IOO 400 00 IOOO 1300 1600 1900 2200 700 IOOO 1300 I60C 1900 2200
NANOMETERS NANOMETERS
Fig. 6—Composite of blue curtains, j is the old curtain and S is the Fig. 7—Comparison of old and new gray curtains (samples C
new curtain. and M)
72-s | MARCH 1979
old
IOOO 1300
io 0 0 400 700 IOOO 1300 1600 1900 2200
NANOMETERS NANOMETERS
Fig. 8—Comparison of old and new green curtains (samples B Fig. 9—Comparison of old and new yellow curtains (samples S
and X) and Q)
(3) Figure 11 suggests the critical wave- plates, it is informative to note the
knXB lengths that cause ocular and skin results (see Table 2). For example, the
biological effects, but does not give comparison indicates that certain
U n d e r t h e a s s u m p t i o n t h a t k a = kb
information on the energy necessary transparent curtains exceed the ab-
e q u a t i o n (3) b e c o m e s :
to produce these effects. Not shown is sorption properties required of a shade
R =^± (4) the American Conference of Govern- 2 lens. It should be noted that all
mental Industrial Hygienists recom- curtain transmission values in the IR
This means that transmittance is a mended exposure level of 1 m W / c m 2 region exceed the values given in ANSI
function of thickness only. If, howev- for the wavelength region between Z87.1. Also, note that only the green
er, equation (4) is not valid, then the 320 and 400 nm. and yellow curtain transmittances ex-
difference in transmittance has to be From a protection viewpoint, the ceed the UV value listed for shade 2. In
explained by more than consideration best curtain w o u l d minimize or elimi- particular, 5 of 11 yellow samples and 3
of thickness. To confirm this observa- nate hazardous wavelengths (i.e., of 7 green samples do not meet shade
tion, transmission values from curtains shaded area). In almost every curtain 2 criteria. Of interest here is that 7 of
having the smallest and largest thick- tested, wavelengths less than about the 8 that failed were new samples. In
nesses of each color were compared. 340 nm were greatly suppressed. This no way should this comparison
The results indicate that w i t h i n experi- fact is very important, since it tends to remotely suggest that it is appropriate
mental errors differences in transmit- suggest that most transparent curtains for the transparent welding curtains to
tance could be explained by thick- give adequate protection in the UV be used as a replacement for welding
ness. region. However, most curtains also safety lens.
transmit at wavelengths beyond 400 A summary spectral transmission
nm which is in the shaded area. There- plot depicting various curtain samples
Discussion fore, as far as overall protection from is shown in Fig. 12. Since most samples
In determining the degree of protec- ocular and skin hazards is concerned tested demonstrated little transmis-
tion offered by transparent curtains, it (i.e., minimizing the shaded area), the sion difference between old and new
is necessary to define the spectral grey curtain w o u l d appear the best curtains, then Fig. 12 was developed
zones that can produce potentially choice. However, if visibility of the using results from only new samples.
hazardous optical radiation biological workplace is paramount, then one Figure 13 shows results provided by
effects. These zones are shown as the might consider the yellow curtain. one of the manufacturers. Note that
shaded area in Fig. 11. Figure 11 was The transmittance results can be Figs. 12 and 13 generally agree w i t h
developed by combining data from compared w i t h the ANSI Z87.1 stan- each other except for the blue curtain
recent publications. 9 - 10 The shaded dard for welding filter plates." Al- transmission values. In this case the
area indicates the relative spectral though this comparison is not neces- blue curtain values are smaller in the
hazards from broadband non-coher- sarily valid since transparent plastic 500-to-800 nm region than those
ent sources, such as a welding process. curtains can not be considered filter reported by the manufacturer.
W E L D I N G RESEARCH S U P P L E M E N T I 73-s
. after
' before
aOO 500 400 500 600 TOO
NANOMETERS
Fig. 11-Envelope (shaded area) of potential
hazardous broadband non-coherent optical
radiation
The results shown in Fig. 12 could be
Fig. 10—Comparison of yellow curtain of vital safety importance in selecting a
(sample R) before and after cleaning transparent curtain for use in other
than welding applications (i e , shield-
ing a UV curing system) However,
since these curtains are intended for
use in the welding environment, the
spectral distribution of optical radia-
tion from various welding processes
transmitted through different curtains
is of occupational concern. Using
current published welding data' 2 and
the spectral transmission values in this
paper, it is possible to estimate the
approximate distribution of optical
radiation transmitted through trans-
parent curtains.
Figure 14 shows the actual and
approximate optical radiation spectral
IOO 400 700 IOOO 1300 1600 1900 2200 irradiance values from a typical w e l d -
NANOMETERS ing process. Figure 15 shows the
product of the approximate irradiance
and transmission values; it was devel-
Table 2 —Transmittance Test Results of Weld ng Curtains Compared with Values Given in
ANSI Z87.1
oped using the same curtain samples
discussed in Fig. 12, w i t h the exception
of the yellow curtain. Since this paper
Spectral transmittance
Infrared finds that older yellow curtains trans-
at selected wavelength, % transmitt ance mit more than new curtains, only older
Sample color 313 nm 334 nm 365 nm 405 nm > 760 n n, %
yellow curtain transmission values are
Shade 1.5 lens 0.2 0.8 25. 65. 25 shown in Fig. 15.
Shade 2.0 lens 0.2 0.5 14. 35. 15
A Curtain yellow 0.03 0.04 10. 23. 86.5"
B Curtain green 0.01 0.02 O.I 2. 43."
Conclusion
C Curtain gray 0 0 0 3. 28." W i t h this particular welding process,
D Curtain yellow 0.03 0.05 5. 7. 78.'"
both old and new yellow curtains
E Curtain green 0 0 0.1 1.6 43.'"
0.7'"' 79."
transmit more optical radiation energy
F Curtain yellow 0.35 16.'" 12.
G Curtain yellow 0 0 10. 22. 94." than other curtains.
H Curtain green 0.04 0.06 0.5 2.0 48." W h i l e the magnitude of optical
I Curtain gray 0 0 0 2.0 23." energy transmitted by a yellow curtain
I Curtain blue 0 0 0 0.1 80.'" is small, the spectral distribution
K Curtain green 0.27'" 0.42 1.0 3. 51." contains a larger component of haz-
L Curtain yellow 0.25"" 6.'"' 3. 0 89." ardous wavelengths than other cur-
M Curtain gray 0 0 0 1. 20." tains. Obviously, additional factors
N Curtain green 0.34"" 0.54"" 0.9 2.1 41."' such as distance from welding arcs
O Curtain yellow 0.23"" 5 ,., 2.0 0 81."
shielding mediums, welding pro-
P Curtain green 0.33"" 0.55"" 1.0 2.3 42."
cesses, etc., have to be considered
Q Curtain yellow 0.22"" 6.0'" 2.5 0 82."
Rr Curtain yellow 0 0 0 0 78." before one could recommend a partic-
R„ Curtain yellow 0 0 0 0 89.'" ular curtain for a certain welding
S,, Curtain blue 0 0 0 0 68.'" event. However, evaluating welding
S;, Curtain blue 0 0 0 0 82." curtains according to welding pro-
T Curtain yellow 0.17 3.6"" 2.0 0 86."' cesses seems more prudent and proper
W Curtain gray 0.01 0.01 0.04 3.0 51." rather than allowing workers/manage-
X Curtain green 0 0 0 2.0 20." ment to select one merely on the basis
Z Curtain yellow 0.02 0.03 7 14. 86."' of eye appeal. In the near future a
" I n d i c a t e values greater than those for Shade 2.
more comprehensive report will be
74-s I M A R C H 1979
ACTUAL
"DATA
400 480 560
NANOMETERS
Fig. 14—Absolute spectral irradiance at 1 m for G T A W welding
process, on steel, 275 A, 'Ar, In. (7.6 mm) arc length, helium shielding
gas
1000 1300 1600 1900
NANOMETERS
Fig. 12—Spectral transmission measurements found in this paper
400 500
WAVELENGH,
Fig. 15-Approximate spectral distribution ot optical radiation
(shaded areas) transmitted through various transparent welding
curtains from GTA welding process
600 800 IOOO I I400 I600
WAVELENGTH(NANOMETERS)
9. American Conference of Governmen-
Fig. 13—Spectral transmission measurements reported by manufac- tal Industrial Hygienists, 1977, Threshold
turer (modified) Limit Values for Chemical Substances and
Physical Agents in the W o r k r o o m Environ-
ment, P.O. Box 1937, Cincinnati, O h i o
45201.
p u b l i s h e d o n t h i s t y p e o f e v a l u a t i o n . It 3. El Gammal, M. Y., Soliman, A. M. and 10. Pitts, D. O , Cullen, A. P., and Hacker,
m u s t b e k e p t in m i n d t h a t o t h e r Mostafa, M. S., "Actinic Conjunctivitis—The P. D., "Ocular Ultraviolet Effects from 295
Effect of UV and IR Radiation on the Eyes nm to 400 nm in the Rabbit Eye," D H E W
c u r t a i n s e l e c t i o n c r i t e r i a , s u c h as b e i n g
of Welders and Glassblowers," Bull Ophth. (NIOSH) Publ. No. 77-175, 1977. National
a b l e t o see t h r o u g h t h e c u r t a i n , m a y
Soc. Egypt, 66/70:41, 1973. Institute for Occupational Safety and
have to be considered. Health, Cincinnati, O h i o 45226.
4. Russ, D. S., "The Short-Term Effects on
W h i l e t h i s p a p e r has d e a l t w i t h Health of Manual Arc W e l d i n g , " I. Soc. 11. American National Standards Insti-
transparent c u r t a i n s , it s h o u l d be Occup. Med., 23/3:92, 1973. tute (ANSI) 1968, American National Stan-
m e n t i o n e d that m u c h m o r e work 5. Hanene, E., and Gutschmidt, E., dard Practice for Occupational and Educa-
n e e d s t o be d o n e w i t h r e f l e c t i v e c h a r - "Squamous Cell Carcinoma in an Electric tional Eye and Face Protection, ANSI Z87.1,
acteristics of o p a q u e curtains. Welder," Berufsdermatosen, 24/5:119, 1430 Broadway, New York, New York
1976. 10018.
6. Filipiakow, Z., "The Influence of 12. Marshall, W. |., et al., Nonionizing
Reterences
W e l d i n g Arc Radiation on the Picture of the Radiation Protection Special Study No. 42-
1. Ruprecht, K. W., "Foveo-Maculopathy Eye Fundus," Klin. Oczna, 40/4:529, 1970. 0312-77, Evaluation of the Potential Retinal
Resulting from Arc W e l d i n g , " Zentralblat 7. Goldman, H., "Genesis of Heat Cata- Hazards from Optical Radiation Generated
Arbeitsmid, 26:200, 1976. ract," Arch. Ophth., 9:314, 1933. by Electric W e l d i n g and Cutting Arcs, 1977,
2. Clark, B. A. )., " W e l d i n g Filters and 8. "What's Happening w i t h W e l d i n g USA Environmental Hygiene Agency, Aber-
Thermal Damage to the Retina," Australian Curtains," Welding Design and Fabrication, deen Proving G r o u n d , M D (NTIS No. A D A
j. Optom., 51:91, 1968. |une:98, 1978. 043023).
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