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Hexone

General Description

Synonyms: 4-Methyl-2-pentanone; Methyl isobutyl ketone; Isobutyl methyl ketone; MIBK

OSHA IMIS code: 1385

CAS number: 108-10-1

Exposure Limits and Health Effects (Updated September 6, 2012)

Standard Set By Exposure Limit Health Effect Codes -- Health Effects and Target Organs
OSHA PEL - General Industry
See 29 CFR 1910.1000 Table Z-1
100 ppm (410 mg/m3) TWA
HE7 -- dizziness, headache, weakness
Target organs: brain, central nervous system
HE8 -- narcosis, coma
HE16 -- eyes, nose, throat, and respiratory irritation; burning eyes
OSHA PEL - Construction Industry
See 29 CFR 1926.55 Appendix A
100 ppm (410 mg/m3) TWA
HE7 -- dizziness, headache, weakness
target organs: brain, central nervous system
HE8 -- narcosis, coma
HE16 -- eyes, nose, throat, and respiratory irritation; burning eyes
OSHA PEL - Shipyard Employment
See 29 CFR 1915.1000 Table Z - Shipyards
100 ppm (410 mg/m3) TWA
HE7 -- dizziness, headache, weakness
target organs: brain, central nervous system
HE8 -- narcosis, coma
HE16 -- eyes, nose, throat, and respiratory irritation; burning eyes
NIOSH REL 50 ppm (205 mg/m3) TWA
75 ppm (300 mg/m3) STEL
HE7 -- dizziness, headache, weakness
target organs: brain, central nervous system
HE8 -- narcosis, coma
HE16 -- eyes, nose, throat, and respiratory irritation; burning eyes
HE16 -- skin irritation, dermatitis
ACGIH TLV® (2009) 20 ppm (82 mg/m3) TWA
75 ppm (307 mg/m3) STEL
A3
BEI®
HE7 -- dizziness, headache, weakness
target organs: brain, central nervous system
HE8 -- narcosis, coma
HE16 -- eyes, nose, throat, and respiratory irritation; burning eyes
CAL/OSHA PELs

50 ppm (205 mg/m3) TWA
75 ppm (300 mg/m3) STEL

Carcinogenic classification:

EPA Inhalation Reference Concentration (RfC): 3 mg/m3

ATSDR Inhalation Minimal Risk Levels (MRLs): Not established

NIOSH IDLH concentration: 500 ppm

Notes on other potential health effects and hazards:

  1. Because hexone's odor is detectable at levels below the REL, hexone is treated as a chemical with adequate warning properties (NIOSH 1988).
  2. Hexone is highly flammable, and vapor/air mixtures can be explosive (NIOSH/IPCS 1997).
  3. The EPA RfC is based on a study showing reduced fetal body weight, skeletal variations, and increased fetal death in mice, and skeletal variations in rats (EPA 2003; Tyl et al. 1987).
  4. Although only a small fraction of the hexone absorbed by the lungs is excreted into urine (~0.12%), the measurement of hexone in urine has been recommended as a biological marker for occupational exposure (Kawai et al. 2003).
  5. One case study with six follow-up exams over a period of 10 years reported a lasting impairment of working memory in a 44-year-old worker with a history of hexone exposure to 100 ppm, with daily excursions to higher (unknown) levels for six years. A co-worker also showed memory deficits (Grober and Schaumburg 2000).
  6. Two-year studies conducted by the National Toxicology Program indicated some evidence of carcinogenic activity of MIBK in male F344/N rats, equivocal evidence of carcinogenic activity  of MIBK in female F344/N rats, and some evidence of carcinogenic activity of MIBK in male and female B6C3F1 mice (NTP 2007).

Partial reference list:

  • ACGIH: Documentation of the Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs) - Methyl Isobutyl Ketone. 2016.
  • EPA: Toxicological review of methyl isobutyl ketone (CAS No. 108-10-1). March 2003.
  • Grober, E. and Schaumburg, H.H.: Occupational exposure to methyl isobutyl ketone causes lasting impairment in working memory. Neurology 54(9): 1853-1855, 2000.
  • Kawai, T. et al.: Methyl isobutyl ketone and methyl ethyl ketone in urine as biological markers of occupational exposure to these solvents at low levels. Int. Arch. Occup. Environ. Health 76(1): 17-23, 2003.
  • NIOSH: Occupational Safety and Health Guideline - Hexone. 1988.
  • NIOSH/CEC/IPCS: International Chemical Safety CardsMethyl isobutyl ketone. July 10, 1997.
  • NTP: NTP Technical Report on the Toxicology and Carcinogenesis Studies of Methyl Isobutyl Ketone (CAS NO. 108-10-1) in F344/N Rats and B6C3F1 mice (Inhalation Studies), February 2007.
  • Tyl, R.W., K.A. France, L.C. Fisher, I.M. Pritts, T.R. Tyler, R.D. Phillips, and E.J. Moran: Developmental toxicity evaluation of inhaled methyl isobutyl ketone in Fischer 344 rats and CD-1 mice. Fundam Appl Toxicol. 8:310-327, 1987.

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