Description
This article is from the Chemistry
FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous
contributions by others.
10.7 Are contact lenses a hazard in laboratories? (Chemical Safety)
There are a lot of myths about the occupational use of contact lenses, many
of which relate back to a Bethlehem Steel welder in Baltimore who, on the
26 July 1967, accidentally caused an arc flash that hit his hard contact
lens. He waited until the next day to report eyesight problems, and an
ophthalmologist found severe ulcerations on his cornea, but attributed
the damage to the wearing of the hard lenses for 17-18 hours after the
incident. The cornea healed completely in a few days, with no permanent
vision loss, and investigators found no link between the damage and the
arc flash, but the myth of the welder removing parts of the cornea with
the lens, and consequently being permanently blinded, continues [14].
The banning of contact lenses from modern chemical laboratories is being
reconsidered in the light of increasing evidence that case-by-case
evaluations are more appropriate. Routine wearers of contact lenses may
suffer " spectacle blur " when they switch to spectacles, and this temporary
reduction in visual efficiency could result in the misreading of labels.
Contact lenses are not eye protection devices, and OSHA believes that
if eye hazards are present, appropriate eye protection must be worn
instead of, or in conjunction with, contact lenses. There may still be some
laboratory environments where the provided personal protection equipment
does not protect wearers of contact lenses, and they will remain banned.
There are three major areas of concern about the hazards of wearing
contact lenses in chemical laboratories.
1. They can hold particulate or liquid material against the cornea.
The modern soft contact lenses are considered suitable for most
environments, except where heavily contaminated with metal particles.
Hard contact lenses are not considered suitable for use in
particle-contaminated areas.
2. Contact lenses can be difficult to remove after a chemical splash.
This is a concern, and is one reason why wearers of contact lenses in
laboratories should be obviously identifiable to first-aid and
professional secondary care providers. The copious irrigation procedures
with water ( whilst holding the eye open ) that should immediately follow
chemical splashes may wash the lenses out, and trained staff can remove
any remaining lenses later. Experiments with concentrated sodium
hydroxide solution, sulfuric acid, acetic acid, acetone and n-butylamine
have shown that contact lenses may actually provide some protection [14].
3. Contact lenses may absorb and retain chemical vapours.
This effect was not observed in the splash experiments above, and soft
lenses have been shown to reduce the effect of acids, perhaps because
tears can dilute the acid by the time it passes through the lens.
Some chemical vapours may be absorbed and retained, but often exposure
should be eliminated by personal protection equipment anyway.
The January/February 1995 issue of Chemical Health and Safety had three
articles on contact lenses, including an excellent article on how to prepare
for, and act during, contact lenses emergencies [15]. All three articles
note that changing technologies have resulted in improved lenses that may
now be acceptable in many modern laboratories, however the merits of each
case should be carefully examined before approval. The issue of contact
lenses in laboratories is still being carefully reviewed, as there are also
legal implications for both employers and employees, and laboratory safety
literature should be monitored to obtain the latest perceptions [16,17].
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