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Methyl acetylene

May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 74–99–7

NIOSH REL: 1,000 ppm (1,650 mg/m3) TWA

Current OSHA PEL: 1,000 ppm (1,650 mg/m3) TWA

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 1,000 ppm (1,640 mg/m3) TWA

Description of substance: Colorless gas with a sweet odor.

LEL :. . 1.7% (10% LEL, 1,700 ppm)

Original (SCP) IDLH: 15,000 ppm [LEL]

Basis for original (SCP) IDLH: The chosen IDLH is based on the lower explosive limit (LEL) of 17,000 ppm rounded down to 15,000 ppm.

Short-term exposure guidelines: None developed


Animal data: None relevant for use in determining the revised IDLH.

Human data: It has been stated that methyl acetylene appears to be a general anesthetic with comparatively low toxicity [ACGIH 1991].

Revised IDLH: 1,700 ppm [LEL]

Basis for revised IDLH: Since methyl acetylene appears to have relatively low toxicity [ACGIH 1991], the revised IDLH is 1,700 ppm based strictly on safety considerations (i.e., being 10% of the lower explosive limit of 1.7%).


1. ACGIH [1991]. Methyl acetylene. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, p. 929.