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C&EN Nov. 19, 1979
Letters
Area can be enormous SIR: Carl R. Blumenstein (C&EN, Oct. 15, page 4) wants to know what fraction of the U.S. will be defaced by strip mining and oil shale mining. His letter reminded me of the following passage: "A large chemical plant using considerable quantities of sulfuric and nitric acids was able to account for 99.99% of the acids used. From the viewpoint of the chemical engineer there was no waste. Yet the effluent from that plant reduced the pH of a stream to 4.0 for 6 miles below the plant" (W. Rudolfs, ed., "Industrial Wastes," American Chemical Society, 1953, page 242). Oil shale and strip mining may affect only a small fraction of the U.S. as seen from space, but at ground level in Wyoming, Colorado, and other fossil fuel-rich areas the amount of affected land could be enormous. Thomas R. Holm Research Associate, University of Wisconsin, Madison
Caution to contact lens users SIR: I am writing in response to Marjorie Kandel's letter (C&EN, Oct. 15, page 43) of request for information with regard to contact lens safety in the chemical laboratory. As a laboratory safety and health consultant, I have found extensive injury and injury potential in chemical laboratory and pilot plant pperations from the use of contact lenses with and without protection. The following areas are but a few indications of the hazard experience to which I refer. It must first be ascertained by the person interested in laboratory safety whether the contact lenses are of the "hard" or "soft" type, what is the history of use for the wearer, and have there existed any prior irritational or corneal abrasion conditions as a result of the current period of wear. The trapping of vapors behind the hard contact lens is augmented in the newer designed "soft" lenses by the entry through the lens of gases and vapors which may dissolve into the tear liquids which are responsible for floating the lens on the eye. The "hard lenses" or cornea lenses are made of polymethyl methacrylate and are generally seven to 10 mm in diameter covering only a part of the cornea. With blinking, this lense has a constant tear flow beneath it, and an incumbent trapping and recirculation of liquids once solubilized in the tear fluid. The soft contact lenses are generally larger, between 12 and 15 mm in diameter and cover a larger area of cornea and part of the sclera as well. These areas for trapping of liquids must be considered based on the potential chemical exposure of the worker. Additional complications for the contact lens wearer in the chemical laboratory is oftentimes the absence of a source of clean water for which
to decontaminate the hands prior to reinstallation or change of contact lens wearing position. The use of contact lenses in a laminar flow air environment can also be considered a hazard potential as it aggravates the dehydration of the tear layer upon which the lens rides, giving rise to subsequent corneal abrasions and other related phenomena. I would direct your reader's attention to two articles which recently addressed this area of safety and health: Dixon, William S., "Contact lenses: do they belong in the workplace?," Occupational Safety & Health, May-June 1978; Allison, William W., "The proper use of eyewash fountains and safety showers," Professional Safety, May 1978. Thank you for the opportunity of commenting on this area of chemical laboratory safety. Kenneth S. Cohen Industrial Hygiene/ Toxicologist, Member, ACS Health & Safety Committee
SIR: In the Oct. 15 issue, Marjorie Kandel asks about wearing contact lenses in the laboratory. As a general rule individuals who consistently wear contact lenses will see better with them than with infrequently used prescription safety glasses, and we believe contact users should be allowed to wear them with additional adequate safety equipment. Although contact lenses have provided some protection in some accidents, contact lenses are not intended as substitutes for properly designed safety eye wear in hazardous situations. The American Optometric Association (7000 Chippewa St., St. Louis, Mo. 63119), from whom more information is available, has adopted a policy statement which reads: "Contact lenses may be worn in hazardous environments with appropriate covering safety eye wear. Contact lenses of themselves do not provide eye protection in the industrial sense (minutes of American Optometric Association Board of Trustees spring interim meeting, March 10, 1977, St. Louis, Mo., page 48). This is a position similar to that taken by the Council on Occupational Health, American Medical Association ("Use of Contact Lenses in Industry," Council on Occupational Health, American Medical Assoc); see J. Am. Med. Assoc, 188, 397 (1964). Every person involved with chemical operations should note that in the majority of instances the correct emergency treatment for chemicals that enter the eye is to wash the injured eye Continued on page 84
Correction • Nov. 5, page 12: Western Europe ethylene plants on average will be operating at less than 80% of their nameplate capacity in 1985, not 8%.
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C&ENNov. 19, 1979
Letters Continued from page 4 thoroughly with plain water for 15 minutes as soon as possible. Attempts to neutralize or counteract the injury may lead to further irritation. Medical attention should be sought for all eye burns. Alkaline materials in the eye are more dangerous than strong acids; acid tends to coagulate protein and form a barrier to further penetration; alkaline materials continue to soak into the tissue. Prolonged washing is needed to remove alkalies. Injurious chemicals may become trapped under contact lenses, which prevent thorough irrigation of the eye. In the event of chemical irritants in the eye, the wearer, if conscious, should remove his/her contact lenses, because the person giving assistance may not know that contact lenses are being worn or how to remove them. Since contact lenses are not protective devices and may increase the chance of injury, the wearer of contact lenses should use the same protective devices worn by other workers. John L. Ennis Irving Arons Arthur D. Little Inc., Cambridge, Mass.
SIR: Marjorie Kandel's letter prompted me to check with one of the faculty members of the ophthalmology department at the University of Wisconsin medical school regarding contacts and chemicals in the eye. I should like to relay the following impressions. If a chemical spill into the eyes occurs, neither the normal tearing mechanism nor external irrigation (with water or saline) is effective in removing chemicals under the contact. The contact must first be removed before tearing or irrigation is effective; however, the contact may be difficult to remove because of the tight squeezing shut of the eye that occurs in response to a chemical in the eye. Since time is of the essence with a chemical burn, a delay caused by the necessity of removing a contact could have serious consequences. Additional hazard is associated with soft contact lenses, which not only are more difficult to remove, but also are more porous (i.e., retaining chemical). It is hoped this will enable both laboratory supervisors and students to make a better informed decision about wearing contacts in the chemical laboratory. Arnold J. Krubsack Medical Student, University of Wisconsin, Madison
SIR: Perhaps I can answer the questions presented by Marjorie Kandel relating to safety with contact lenses. Contact lenses do present an increased hazard to the wearer in the chemical laboratory, especially in the event of a chemical eye-splash. Rigid contact lenses are constructed of such materials as polymethyl methacrylate, cellulose-acetatebutyrate and methyl methacrylate-silicone copolymers; all soluble in or swollen by many organic solvents. The "soft" lenses are constructed of various water-swollen
cross-linked polymers. In addition to the damage to the substrate and uptake of organic solvents, aqueous chemical solutions are readily soluble in the water phase of the soft lenses. Should a chemical eye-splash occur, the contact lenses will, in most cases, increase the concentration of chemical(s) in contact with the eye, resulting in more trauma to the eye. Even if there is no direct eye damage from chemical contact, the contact lens can be rendered useless and may become an eye hazard as a result of distortion or contamination. Soft lens wearers commonly exhibit protracted eye irritation from low concentrations of cigarette smoke and the really toxic vapors common to the laboratory can cause severe reactions. I have a number of patients with contact lens problems directly attributable to vapor exposure in the chemical laboratory and the workplace. Irritating substances in the eye cause a reflex blepharospasm. This clamping together of the eyelids can make removal of contact lenses almost impossible without general anesthesia. To further complicate matters, the contact lenses may be entirely forgotten in the light of crisis. Irrigation of the eye to remove the offending substance is ineffective with the contact lens in the eye, increasing concentration and contact time of the contaminant. Contact lenses should be replaced with prescription safety glasses in all but a few rare instances when eye hazards are present. Richard D. Rowe, O.D. Commerce, Tex.
SIR: In a letter published in your Oct. 15 issue, Marjorie Kandel appealed for information regarding the hazards, if any, of wearing contact lenses in the laboratory. The question seems to be answered fairly well on pages 96 and 97 of the "Handbook of Laboratory Safety" (2nd Ed., N. V. Steere, Editor, Chemical Rubber Co., 1971), including a revealing color photograph. Chemicals splashed into the eye or dissolved in tears from vapors will creep in (apparently by capillary action) under contact lenses. They are held in place by the lens so that they are not rinsed away by normal tear action or by irrigation, unless the contact lens is removed. Soft contact lenses present an even more serious hazard. Any chemical that comes in contact with such a lens can diffuse into the interior of the lens, which then acts as a reservoir that can create additional exposure, even if the lens is removed and rinsed when the eye is irrigated. Soft contact lenses are sometimes used for application of medication to the eye by slow diffusion, and it is fairly obvious that harmful chemicals can enter the eye in exactly the same way. If students or others working with chemicals have eye conditions that actually require the wearing of contact lenses, those individuals should be warned that wearing of contact lenses could be harmful to their visual health. I find that when I have explained these facts, even to beginning freshman students, they have always been willing and able to function with prescription glasses, though possibly not as well as with contact lenses. George G. Lowry Professor of Chemistry, Western Michigan University, Kalamazoo
