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SODIUM HYDROXIDE								Related Pages
										*OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.*
**CAS:** 1310-73-2; **Chemical Formula:** NaOH
The former OSHA limit for sodium hydroxide (also known as caustic soda or lye) was 2 mg/m3 as an 8-hour TWA. OSHA proposed a 2-mg/m3 ceiling limit for sodium hydroxide, based on the ACGIH- and NIOSH-recommended limits. NIOSH (Ex. 8-47, Table N1) concurred with the proposed limit, and this limit is established in the final rule. Sodium hydroxide is a white, deliquescent solid.
Sodium hydroxide is a severe irritant of the eyes, mucous membranes, and skin. Exposure to sodium hydroxide in the form a caustic dust irritates the upper respiratory tract and may cause ulceration of the nasal passages (ACGIH 1986/Ex. 1-3, p. 535). Although inhalation of sodium hydroxide is usually of secondary importance in industrial exposures, the effects of inhaling the dust or mist vary from mild irritation of the nose, which occurs on brief exposure to 2 mg/m3, to severe pneumonitis, which occurs at very high exposures. The greatest industrial hazard is rapid tissue destruction of the eyes or skin upon contact either with the solid or with concentrated solutions (Chemical Hazards of the Workplace, 2nd ed., p. 444, Proctor, Hughes, and Fischman 1988).
Contact with the eyes causes disintegration and sloughing of conjunctival and corneal epithelium, corneal opacification, marked edema, and ulceration; after 7 to 13 days, either gradual recovery begins or there is a progression to ulceration and corneal opacification. Complications of severe eye burns are symblepharon with overgrowth of the cornea by a vascularized membrane, progressive or recurrent corneal ulceration, and permanent corneal opacification (Proctor, Hughes, and Fischman 1988, p. 444). Grant (1986/Ex. 1-975) states that sodium hydroxide causes “some of the most severe, blinding injuries of the eye. Because it may be considered public enemy number one for causing chemical burns of the eye, sodium hydroxide has been the chemical caustic most extensively studied in animal and clinical investigations.” Clinically, the worst features of sodium hydroxide burns of the eye are the great rapidity with which extreme damage can be done to the anterior segment of the eye and the tendency for the cornea to ulcerate and perforate or to become densely vascularized and opaque.
On the skin, solutions of 25 to 50 percent sodium hydroxide cause the sensation of irritation within about three minutes; with solutions of 4 percent, the sensation of burning does not occur until several hours later. If not removed from the skin, sodium hydroxide causes severe burns with deep ulcerations. Exposure to the dust or mist of sodium hydroxide may cause multiple small burns with temporary loss of hair (Proctor, Hughes, and Fischman 1988, p. 445). Nagao and co-workers (1972) examined skin biopsies from volunteers who had had a 1 N solution (equal to a 4-percent solution) of sodium hydroxide applied to their arms for 15 to 180 minutes. Progressive changes, beginning with dissolution of the cells in the horny layer and progressing through edema to total destruction of the epidermis, occurred within 60 minutes (Nagao, Stroud, Hamada et al. 1972).
Rats were exposed to an aerosol of 40 percent aqueous sodium hydroxide whose particles were less than 1 um in diameter. Exposures lasted for 30 minutes and were administered twice a week. The experiment was terminated after three weeks because two of the 10 rats died. Histopathological examination showed mostly normal lung tissue with foci of enlarged alveolar septae, emphysema, bronchial ulceration, and enlarged lymph adenoidal tissues (Wands 1981b, in Patty’s Industrial Hygiene and Toxicology, 3rd rev. ed., vol. 2B, p. 3062).
OSHA received only one comment on sodium hydroxide, from NIOSH (Ex. 150, Comments on Sodium Hydroxide); NIOSH supported OSHA’s proposed limit and reported that no new information on the health effects of sodium hydroxide had become available since the publication of the NIOSH criteria document (NIOSH 1976k/Ex. 1-965).
The irritant effect of sodium hydroxide and its markedly corrosive action on all body tissue can result even from brief (one minute or more) exposures to airborne concentrations above the 2-mg/m3 level; the acute nature of these effects is evident in the studies described above. Therefore, OSHA concludes that establishing a ceiling of 2 mg/m3 is necessary to reduce the significant risks of eye and skin burns and respiratory irritation that occur as a result of very brief exposures to the higher levels of sodium hydroxide that would be permitted with an 8-hour TWA PEL alone. OSHA considers the irritant effects resulting from exposure to sodium hydroxide material impairments of health. In the final rule, OSHA is accordingly revising its former 8-hour TWA limit for sodium hyroxide to a ceiling limit of 2 mg/m3.
										
							
								Page last reviewed:  September 28, 2011						Content source:  	National Institute for Occupational Safety and Health NIOSH
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