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: 110-91-8; Chemical Formula: C4H9NO

OSHA had a limit of 20 ppm, with a skin notation, for morpholine. The ACGIH has a 20-ppm TWA limit and a TLV-STEL of 30 ppm, as well as a skin notation. The proposal retained the 8-hour TWA PEL of 20 ppm and added a STEL of 30 ppm; NIOSH concurs that these limits are appropriate (Ex. 8-47, Table N1), and they are established in the final rule. The skin notation is retained. Morpholine is a colorless liquid with an amine-like odor.

Exposure to morpholine produces nasal and bronchial irritation and liver and kidney impairment in animals (Shea 1939/Ex. 1-758); the substance readily penetrates the skin and is highly irritating to the eyes (Jefferson Chemical Company, Inc. 1961, as cited in ACGIH 1986/Ex. 1-3, p. 417). The single oral LD(50) in rats is 1.05 g/kg (range: 0.95 to 1.16 g/kg), and the single skin LD(50) for 24-hour contact is 0.5 ml/kg (Smyth, Carpenter, Weil, and Pozzani 1954/Ex. 1-440). Neither a one-hour exposure to concentrated vapor nor an 8-hour exposure to 8000 ppm was fatal in rats (Smyth, Carpenter, Weil, and Pozzani 1954/Ex. 1-440). Rats were exposed for eight hours daily to a concentration of 18,000 ppm for a total of five days; after the first day, all animals showed severely reddened thoracic walls, and one fatality (from kidney and liver congestion) occurred. A similar fatality occurred on the third day; on day 4, a third rat died, and postmortem examination revealed degeneration of the epithelial lining of the kidney tubules. Three additional deaths occurred after the exposures had ended; autopsy revealed thickened alveoli, emphysema, and liver and kidney effects (Shea 1939/Ex. 1-758).

Reporting on his own reactions to morpholine exposure at a concentration of 12,000 ppm, Shea (1939/Ex. 1-758) complained of nose irritation (after 1 minute) and coughing (after 90 seconds); in addition, when he transferred morpholine by pipette, he experienced sore throat and mucosal irritation. All symptoms disappeared after the experiment stopped (Shea 1939/Ex. 1-758). Skin contact poses a moderately high degree of hazard, which diminishes as the product is diluted with water to less than 25 percent (Jefferson Chemical Company, Inc. 1961, as cited in ACGIH 1986/Ex. 1-3, p. 417). Respiratory irritation but no chronic effects have been reported as a result of industrial exposure (Patty 1963e/Ex. 1-858). In comparison with ammonia, morpholine has a greater potential for systemic toxicity (ACGIH 1986/Ex. 1-3, p. 417).

OSHA received a comment on morpholine from Lawrence Hecker of Abbott Laboratories (Ex. 3-678). Dr. Hecker states (Ex. 3-678, p. 8) that the STEL proposed for morpholine should not be included in the final rule because the health evidence for this substance does not warrant a STEL. OSHA does not agree with Dr. Hecker; there is evidence in the record that morpholine’s effects are experienced even at elevated exposures lasting only one minute (Shea 1939/Ex. 1-758). Because morpholine has a greater potential for systemic effects than does ammonia, a STEL is needed to ensure that short-term excursions substantially above the 8-hour TWA PEL do not occur.

In the final rule, OSHA is retaining the 8-hour TWA limit for morpholine of 20 ppm TWA and the skin notation, and is adding a 15-minute STEL of 30 ppm. The Agency concludes that these limits will work together to protect workers against the significant risk of eye and respiratory tract irritation, which are material impairments of health that are associated with exposures at levels above the 8-hour TWA limit. OSHA is retaining the skin notation for morpholine because of this substance’s ability to be absorbed through the skin in toxic amounts.

Page last reviewed: September 28, 2011