NIOSH Pocket Guide to Chemical Hazards

Hydrogen cyanide

CAS 74-90-8


RTECS MW6825000
Synonyms & Trade Names
Formonitrile, Hydrocyanic acid, Prussic acid
DOT ID & Guide
1051 117 (>20% solution)
1051 117 (anhydrous)
1613 154 (< or =20% solution)


NIOSH REL: ST 4.7 ppm (5 mg/m3) [skin]
OSHA PEL†: TWA 10 ppm (11 mg/m3) [skin]
IDLH 50 ppm See: 74908 Conversion 1 ppm = 1.10 mg/m3
Physical Description
Colorless or pale-blue liquid or gas (above 78°F) with a bitter, almond-like odor. [Note: Often used as a 96% solution in water.]
MW: 27.0
BP: 78°F (96%)
FRZ: 7°F (96%)
Sol: Miscible
VP: 630 mmHg
IP: 13.60 eV

Sp.Gr: 0.69
Fl.P: 0°F (96%)
UEL: 40.0%
LEL: 5.6%

Class IA Flammable Liquid Flammable Gas
Incompatibilities & Reactivities
Amines, oxidizers, acids, sodium hydroxide, calcium hydroxide, sodium carbonate, caustics, ammonia [Note: Can polymerize at 122-140°F.]
Measurement Methods
NIOSH 6010, 6017
See: NMAM or OSHA Methods
Personal Protection & Sanitation (See protection)
Skin: Prevent skin contact
Eyes: Prevent eye contact
Wash skin: When contaminated
Remove: When wet (flammable)
Change: No recommendation
Provide: Eyewash, Quick drench
First Aid (See procedures)
Eye: Irrigate immediately
Skin: Water flush immediately
Breathing: Respiratory support
Swallow: Medical attention immediately
Important additional information about respirator selection
Respirator Recommendations NIOSH
Up to 47 ppm:
(APF = 10) Any supplied-air respirator
Up to 50 ppm:
(APF = 25) Any supplied-air respirator operated in a continuous-flow mode
(APF = 50) Any self-contained breathing apparatus with a full facepiece
(APF = 50) Any supplied-air respirator with a full facepiece
Emergency or planned entry into unknown concentrations or IDLH conditions:
(APF = 10,000) Any self-contained breathing apparatus that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode
(APF = 10,000) Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained positive-pressure breathing apparatus
(APF = 50) Any air-purifying, full-facepiece respirator (gas mask) with a chin-style, front- or back-mounted canister providing protection against the compound of concern/Any appropriate escape-type, self-contained breathing apparatus
Exposure Routes inhalation, skin absorption, ingestion, skin and/or eye contact
Symptoms Asphyxia; lassitude (weakness, exhaustion), headache, confusion; nausea, vomiting; increased rate and depth of respiration or respiration slow and gasping; thyroid, blood changes
Target Organs central nervous system, cardiovascular system, thyroid, blood
See also: INTRODUCTION   See ICSC CARD: 0492   See MEDICAL TESTS: 0117