Eye Exposure to Optical Radiation in the Glassblowing Industry: An Investigation in Southern Ontario

Abstract

To investigate if the levels of optical radiation hazards in glassblowing are well classified according to the hazard types defined in the Canadian Standards Association (CSA) standard for industrial eye protectors.
We carried out radiometric measurements, and questionnaire survey in 4 university glassblowing laboratories, and 3 private studios.
There is exposure to low levels of UV and IR radiation in all glassblowing operations. A supra-threshold IR radiation level exists in the craft glassblowing. The use of eye protectors is based on past experience regardless of the level of ocular exposure.
Optical radiation hazards exist in both craft and scientific glassblowing. There seems to be an inadequate understanding about radiation types encountered by glassblowers.

Full text

NOVEMBER – DECEMBER 2000 CANADIAN JOURNAL OF PUBLIC HEALTH 471
Glassblowing is a well-established indus-
try which involves the shaping of a mass of
glass into any form after the glass material
has been heated to a viscous state. A wide
variety of glass materials such as silica,
soda-lime, potash, boron, quartz, and
cobalt are handled in glassblowing. Eye
care practitioners and industrial hygienists
need to be able to advise on occupational
eye safety and protection, based on an ade-
quate knowledge of the noxious agents in
the work environment. Glassblowing con-
sists mainly of craft and scientific types,
which use furnace and lathe heating sys-
tems, respectively. Optical radiation is
encountered in glassblowing.
Optical radiation refers to that portion
of the electromagnetic spectrum (EMS)
ranging in wavelengths from 100 to
10x106nm.1The different subdivisions of
the optical radiation spectrum are shown
in Table I. For convenience, wavelengths
from 315 to 400 nm, and 700 to 1100 nm
are designated as near-UV and near-IR
radiation, respectively. Considerable haz-
ardous levels of optical radiation are
encountered in glassblowing operations
daily.2-9 The harmful effects of the long-
term ocular exposure to cumulative levels
of radiation in glassblowing have been rec-
ognized since the late 19th century.2These
effects include cataracts, pterygia, keratitis
and chronic dry eye problems. The total
optical radiation received by glassblowers
working near melting furnaces for approxi-
mately 8 hours daily was reported to be
within the range of 2000 to 3000 J/cm2.
Approximately 10% of the total was in the
near infrared (IR-A) waveband below
1400nm.10 Matelsky (1968)11 reported that
after daily exposure to IR irradiance at
0.08 to 0.4 W/cm2for 10 to 15 years,
some glass and steel workers developed
cataracts.
Apart from corneal and lenticular dam-
age due to near-UV and near-IR, radiation-
induced retinopathy also could occur from
exposure to near-UV, and short wave-
length visible radiation without a signifi-
cant increase in the local temperature of
the irradiated tissue.12 For both short- and
long-term safety, maintaining effective
safety guidelines is critical in any work-
place. As industrial processes change with
technological advancement, the associated
workplace hazards and protective measures
need to be reassessed regularly. The litera-
ture provides few assessments of optical
radiation hazards and ocular protection in
glassblowing operations. The available cen-
sus figures indicate that there are over
1,250 glassblowers (male 1,070; female
180) in Ontario.13 The number of glass-
blowers in southern Ontario could not be
obtained in the government occupational
category publication since most glassblow-
ing installations employ fewer than 5 staff.
Judging by the widely used end-products
including decorative glass wares, light
bulbs such as lead Osram-sylvania SG10,
SG12, and Phillip lead glass replacement
(barium-strontium) lamps, glassblowing is
an integral occupational and public health
aspect of society.
In the present study, we used the
American Conference of Governmental
Industrial Hygienists (ACGIH) recom-
ABSTRACT
Objective: To investigate if the levels of
optical radiation hazards in glassblowing are
well classified according to the hazard types
defined in the Canadian Standards
Association (CSA) standard for industrial eye
protectors.
Methods: We carried out radiometric mea-
surements, and questionnaire survey in 4
university glassblowing laboratories, and 3
private studios.
Results: There is exposure to low levels of
UV and IR radiation in all glassblowing
operations. A supra-threshold IR radiation
level exists in the craft glassblowing. The use
of eye protectors is based on past experience
regardless of the level of ocular exposure.
Conclusions: Optical radiation hazards
exist in both craft and scientific glassblowing.
There seems to be an inadequate understand-
ing about radiation types encountered by
glassblowers.
ABRÉGÉ
Objectif : Étudier si les niveaux des radia-
tions électromagnétiques dangereux dans
l’industrie de soufflage de verre sont bien
documentés et conformes aux normes
actuelles de la CSA (Canadian Standards
Association), afin de déterminer si les souf-
fleurs de verres utilisent adéquatement des
protecteurs oculaires.
Méthodes : Des mesures radiométriques
ont été prises dans quatre laboratoires univer-
sitaires de soufflage de verre et trois studios
professionnels privés.
Résultats : Il y a un niveau relativement bas
de radiation ultraviolet (UV) et infrarouge
(IR) dans toutes les étapes de soufflage de
verre, cependant il existe un niveau d’exposi-
tion plus élevé d’infrarouge dans le soufflage
de verre au milieu professionnel. L’utilisation
des protecteurs oculaires est basée sur l’his-
torique et non sur le taux d’exposition ocu-
laire.
Conclusions : Les dangers reliés aux radia-
tions électromagnétiques existent aux deux
niveaux de l’industrie de soufflage de verre,
notamment scientifique et professionnel. Les
souffleurs ont une compréhension insuf-
fisante envers l’utilisation des lunettes protec-
trices et les différents types de radiation.
Eye Exposure to Optical Radiation in
the Glassblowing Industry: An
Investigation in Southern Ontario
Olanrewaju M. Oriowo, PhD, B. Ralph Chou, MSc, OD,
Anthony P. Cullen, OD, PhD
Optical Radiation Laboratory, School of Optometry,
University of Waterloo, Waterloo, ON
Correspondence and reprint requests: Olanrewaju
M. Oriowo, PhD, Optical Radiation Laboratory,
School of Optometry, University of Waterloo,
Waterloo, ON, N2L 3G1, Tel: 519-885-1211 ext.
3822, Fax: 519-725-0784, E-mail: Loriowo@sci-
borg.uwaterloo.ca
Disclaimer: Authors have no commercial interest in
any products mentioned in this article.

OPTICAL RADIATION HAZARD IN GLASSBLOWING
472 REVUE CANADIENNE DE SANTÉ PUBLIQUE VOLUME 91, NO. 6
mended threshold limits14 for daily UV
and IR radiation exposure to compare our
on-site radiation measurements. Industrial
hazards are classified in the CSA Z94.3-99
standard as following: group A (flying
objects), B (flying particles, dust and
wind), C (heat, glare, sparks, and splash
from molten metal), D (acid splash and
chemical burns), E (abrasive blasting mate-
rials), F (glare, stray light requiring slight
reduction of optical radiation), G (injuri-
ous optical radiation requiring moderate
reduction), and H (injurious optical radia-
tion requiring large reduction).1The CSA
standard (CSA-Z94.3-99)1is similar to the
American National Standards Institute
(ANSI) Z87.1 standard for occupational
eye protection. The ANSI Z87.1 stan-
dard15 lacks specific information on glass-
blowing. The CAN/CSA-Z94.3-991
addresses performance requirements for
industrial eye and face protectors mainly in
craft (artistic) glassblowing operations,
without consideration for scientific glass-
blowing. The present study conducted on-
site radiation measurements, and assessed
whether glassblowing activities are ade-
quately classified under CSA hazard type
definitions. The CSA hazards classification
is used as the basis for selecting industrial
eye and face protection against optical
radiation (e.g., Appendix A of CSA-Z94.3-
99).
MATERIALS AND METHODS
Participating glassblowing installations
were recruited through advertisements in
local newspapers, the internet, and tele-
phone solicitations. Study questionnaires
and informed consents were mailed or
delivered by hand to all the respondents,
with a 70% response rate (out of 10 glass-
blowing sites visited, only 7 agreed to par-
ticipate). This study followed the Helsinki
declaration and was approved by the
University of Waterloo Office of Research.
Scheduled visits were arranged with the
participating sites, the purpose of which
was to assess: 1) the nature of the glass-
blowing task, 2) visual demand and prox-
imity of workers’ eyes to radiation sources,
3) types of glass materials handled, and
4) the emission spectra of radiation
encountered in the different glassblowing
operations. Radiation measurements were
carried out in 4 university and 3 private
glassblowing installations using a spectro-
radiometer (LI-COR Inc., Lincoln, NE,
USA). The operating waveband of our
spectroradiometer ranged from 300 to
1100 nm, which is sufficient for assessing
ocular exposure to optical radiation since
the cornea is opaque to wavelengths below
295 nm and above 1350 nm.16,17 Also, an
aversion mechanism which will normally
result from any slight corneal discomfort
and reflex tearing would reduce the effect
of near-IR radiation longer than ~1100
nm. It has been shown that all available
glassblowers’ eye protectors absorb or cut
off wavelengths below 315 nm.9During
radiation measurements, an aluminum-
coated heat reflector was used at all furnace
installations to protect the radiometer from
thermal damage. The radiometer was posi-
tioned 50 cm from the molten glass mater-
ial, i.e., approximately the same position as
the workers’ eyes. The normal glassblowing
operation was performed for each radio-
metric scan. Scans were made across the
waveband 300 to 1100 nm at 5 nm inter-
vals. Three measurements were taken for
each of the glass materials in their molten
state at all the participating installations.
To determine the levels of workplace ocu-
lar hazard due to optical radiation sources,
the ACGIH guidelines14 were followed.
Results from our representative radiation
measurements were used to determine the
CSA hazard classification for glassblowing,
considered in relation to ACGIH14 recom-
mended exposure limits.
RESULTS
The irradiation values (in W/cm2/nm)
obtained from the different glassblowing
operations are shown in Table II. The
results were analyzed using analysis of vari-
ance (ANOVA) and Student-Newman-
Keul tests. For the statistical analysis to be
valid, it was assumed the radiometric data
were independent and random. The radi-
ant emission spectra of the different glass
materials are reported elsewhere.9The sci-
entific glassblower uses lathe and tabletop
heating systems, while the craft glassblower
uses furnace system to melt or reheat the
glass materials. Our survey revealed that
only 66% of the glassblowers used eye pro-
tection 100% of the time. Eye protector
usage among glassblowers is based on past
experience regardless of the level of radiant
emission from a particular molten glass
material.9
Furnace works are classified under haz-
ard groups F and G in the Canadian
Standard (CSA-Z94.3-99)1for industrial
eye and face protection, but neither craft
nor scientific glassblowing is specifically
listed. Table II shows the comparisons
between the calculated glassblowing irradi-
ation levels and the ACGIH recommended
threshold limit values (TLVs).14 In the
near-UV wavelengths (315-400 nm), all
glass materials emitted UV irradiation at
levels one tenth the TLVs. In the visible
wavelengths (400-700 nm), all glass mate-
rials produced irradiance levels significant-
ly higher than the TLVs (Table II). In the
near infrared, only soda-lime glass has irra-
diance levels about 4 times higher than the
TLVs.
DISCUSSION
The statistical analyses indicated that
the four glass materials observed in this
study (i.e., soda-lime, borosilicate, quartz
and cobalt) produced irradiance levels
which are significantly different (p=
0.0001) from each other. This would
indicate that ocular exposure is different
across the glass materials, which might
invariably imply that different types of
eye protector would be required for dif-
ferent glass materials. Craft glassblowing
operations are classified under hazard
TABLE I
Illustrating the Divisions of the
Optical Portion of Electromagnetic
Spectrum
Wavelength (nm) Divisions
Below 100 X and γrays
100 - 200 Vacuum UV
200 - 280 UV-C
280 - 315 UV-B
315 - 400 UV-A
400 - 700 Visible
700 - 1400 IR-A
1400 - 3000 IR-B
3000 - 10x106IR-C
Note: For the purpose of clarity in this com-
munication, wavelengths within UV-A and IR-
A divisions will be referred to as near-UV and
near-IR, respectively.

groups F & G in the CSA-Z94.3-99 stan-
dards.1Hazard groups C and H are other
classifications in the CSA standard that
can apply to glassblowing. In our survey
we found that soda-lime glass is the main
material handled by craft glassblowers,
while scientific glassblowers handled
quartz, borosilicate and cobalt materials.
Review of the literature reveals that no
previous attention has been specifically
given to scientific glassblowing in the
optical radiation hazard classification.
Our results show that the irradiance levels
from the near UV (315 to 400 nm) wave-
lengths for the glass materials (Table II)
are below the threshold limits (TLVs) rec-
ommended by ACGIH.14 However, in the
visible spectrum (~400 to 700 nm), all
the molten glass materials produced high
intensity visible light greater than the
TLVs. This high intensity visible light
may be sufficient to cause chronic retinal
damage in an unprotected eye. In the
near-IR waveband (~700 to 1100 nm),
irradiance levels from the heating furnaces
were higher than the near-IR TLVs. The
quartz glass material, which demonstrated
a continuum of spectral emission across
the wavelength region, produced the
highest irradiance levels of the glass mate-
rials used in scientific glassblowing. Of all
materials used in both craft and scientific
glassblowing, soda-lime produced the
highest near-UV, visible and near-IR radi-
ation. Previous investigations have con-
firmed that UV and IR irradiation could
cause photokeratitis, cataract, and chronic
retinal injury.12,16-18 Thus retinal damage
due to chronic exposure from high inten-
sity visible light, such as is often encoun-
tered in glassblowing, can occur. Molten
soda-lime material produces suprathresh-
old IR, and a low level of near-UV radia-
tion, which also could cause chronic
corneal, lenticular and retinal damage in
an inadequately protected eye.
Our findings show that exposure to
optical radiation differs in the scientific
and craft glassblowing operations and that
optical radiation hazards exist in both types
of glassblowing. The data showing sub-
stantially low levels of near-UV, high
intensity visible, and high near-IR radia-
tion, suggest that scientific glassblowing
should be classified under CSA hazard
groups C, F and G, and craft glassblowing
under groups C, G and H. Hazard groups
C and F include heat and hot dipping,
however, it should be noted that glare and
stray light present potential hazards in sci-
entific glassblowing operations as well. In
the visible and near-IR regions of the opti-
cal spectrum, all the glass materials used in
this study produce irradiance levels higher
than the ACGIH TLVs. For instance, the
molten soda-lime, a glass material com-
monly used in furnace operation, produces
emissions with resultant irradiation more
than 4 times higher than the TLVs both in
the visible and the near-IR wavebands.
Near-UV penetrates the cornea and is
almost totally absorbed by the lens.
Photokeratitis may result within several
hours after exposure to the low near-UV
irradiation from quartz, borosilicate and
soda-lime materials.
Cataracts, which develop slowly in the
lens, would require high UV and IR irradi-
ance levels, usually from repetitive expo-
sure. It can be argued that the near-IR irra-
diation from molten soda-lime glass mater-
ial may cause cataract if the eye is unpro-
tected. Thus, effective ocular protection
against long-term radiation exposure in the
glassblowing industry is necessary. In an
earlier publication, we found that there is
confusion among glassblowers over what
type of eye protector to use when working
with certain glass material.9We reported
that 80% of glassblowers use didymium
lenses for working with all types of glass
materials, and 20% use welders lenses,
polycarbonate and cobalt lenses inter-
changeably with didymium lenses.
Didymium lenses effectively eliminate the
yellow sodium glare from molten borosili-
cate and other glass materials to enhance
visibility. However, it provides no protec-
tive absorption of near-IR irradiation
encountered in furnace glassblowing opera-
tions. A didymium spectacle with a filter-
weld™ clip-on would be protective. A
summary of suggested eye protection for
glassblowing operations is presented in
Table III.
OPTICAL RADIATION HAZARD IN GLASSBLOWING
NOVEMBER – DECEMBER 2000 CANADIAN JOURNAL OF PUBLIC HEALTH 473
TABLE II
The Spectral Irradiance Values (Within the Near-UV, Visible and Near-IR
Wavebands) of the Molten Glass Materials Compared to the American
Conference of Governmental Industrial Hygienists Recommended Threshold
Limit Values (TLV)
Glass Material/Irradiance (W/cm2)
Waveband (nm) TLV (W/cm2)Borosilicate Cobalt Quartz Soda-lime
315-400 (near-UV) 1.00 X 10-3 0.10 X10-3 0.11 X 10-3 0.14 X 10-3 0.154 X 10-3
400-700 (light) 1.00 X 10-6 5.40 X 10-6 1.32 X 10-6 11.40 X10-6 3.80 X 10-6
700-1100 (near-IR) 10.00 X 10-3 0.60 X 10-3 0.13 X 10-3 1.80 X 10-3 38.50 X 10-3
Adapted from Oriowo, Chou and Cullen, 19979
TABLE III
Suggested Recommended Protective Eye Wear for Glassblowing Operations
Recommended Eye Protection
Glassblowing Type Glass Material Low/Medium Heating High Heating
Craft Soda-lime Filterweld (≥2.5)* Filter weld (≥2.5)*, or
Calobar lenses
Scientific Borosilicate Didymium lenses Didymium with
transparent UV & IR
cut-off filters
Scientific Quartz Filterweld (≥2.5)*, Calobar, Same as under medium
copper-plated face shield heating
Scientific Cobalt Didymium lenses Didymium with
UV & IR filters
Note: A type of effective IR and UV radiation filter is polycarbonate which is vacuum deposited with
a copper metallic coating, and overlayed with quartz for durability. This provides 100% protection
against UV radiation down to 280 nm and 96% protection against IR radiation up to 5000 nm. To
control for any intense visible radiation, the polycarbonate lens may be dyed any colour.19
*Protective lenses with shade number equal or greater than 2.5 is advised.

OPTICAL RADIATION HAZARD IN GLASSBLOWING
474 REVUE CANADIENNE DE SANTÉ PUBLIQUE VOLUME 91, NO. 6
SUMMARY
The results of our investigation demon-
strate differences between craft and scien-
tific glassblowing operations. For the dif-
ferent glass materials, variation exists in the
levels of ocular exposure to optical radia-
tion in glassblowing (p= 0.0001). There is
uncertainty among glassblowers about
what type of eye protector is effective.
Thus, worker’s training about ocular pro-
tection is suggested. The CSA selection
guideline should be revised to include both
craft and scientific glassblowing specifical-
ly.
ACKNOWLEDGEMENTS
We gratefully acknowledge the research
grants from Beta Sigma Kappa (USA), and
the Canadian Optometric Educational
Trust Fund. We thank the British
Columbia Association of Optometrists and
Vision Ease Incorporation for their sup-
port as well as all the participating glass-
blowers.
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Received: September 1, 1998
Revised article received: April 21, 2000
Accepted: May 11, 2000