N-ETHYLMORPHOLINE

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: 100-74-3; Chemical Formula: C₆H₁₃NO

OSHA’s former 8-hour TWA PEL for N-ethylmorpholine was 20 ppm, with a skin notation. The proposed permissible exposure limit was 5 ppm as an 8-hour TWA, also with a skin notation, and the final rule establishes this limit and retains the skin notation, which is consistent with the limits of the ACGIH. NIOSH (Ex. 8-47, Table N1) agrees with the selection of this limit. N-Ethylmorpholine is a colorless, flammable liquid with an ammonia-like odor; this substance is a severe eye irritant.

Prolonged exposure to fairly low concentrations of this substance causes corneal edema, blue-gray vision, and colored haloes. Typically, vision becomes misty and haloes appear a few hours after workers have been exposed to the vapors for a period of hours. Distortion of vision can occur even at levels considerably lower than those that cause irritation (Mastromatteo 1965/Ex. 1-146).

Reversible corneal edema has been observed in workers exposed to 40 ppm or more of N-ethylmorpholine for several hours (Dernehl 1966a/Ex. 1-62). Workers routinely exposed to 3- to 4-ppm concentrations but never to concentrations above 11 ppm complained of haloes and foggy vision as well as drowsiness (ACGIH 1986/Ex. 1-3, p. 263). The irritant effects of N-ethylmorpholine were also seen in a controlled-exposure experiment on volunteer subjects. Ten subjects exposed for 2.5 minutes to a concentration of 100 ppm experienced irritation of the eyes, nose, and throat; those exposed for 2.5 minutes to 50 ppm experienced slight irritation; and no irritation was reported after exposure for 2.5 minutes to 25 ppm (ACGIH 1986/Ex. 1-3, p. 263). N-ethylmorpholine is also readily absorbed through the skin (Smyth, Carpenter, Weil, and Pozzani 1954/Ex. 1-440).

OSHA’s former 20-ppm PEL for N-ethylmorpholine did not protect exposed workers against the occurrence of corneal edema. Because corneal edema is painless as it is developing and symptoms have a delayed onset, workers are especially likely not to be aware of the danger of exposure. This is particularly hazardous because the effects on visual function of repeatedly exposing the eyes to substances that cause corneal edema are not known. The Agency received no comments on the health effects or revised exposure limits for N-ethylmorpholine, with the exception of NIOSH’s submission.

OSHA concludes that reducing the PEL to 5 ppm as an 8-hour TWA (and retaining the skin notation) is necessary to protect occupationally exposed workers from ethylmorpholine’s injurious ocular effects. The new, lower PEL will reduce the significant risk of material health impairment, which is manifested as corneal edema, visual distortion, and impaired vision, that is associated with exposure to this substance at concentrations above the revised PEL.