# NIOSH Pocket Guide to Chemical Hazards
Hydrogen cyanide | CAS 74-90-8
HCN | RTECS MW6825000
Synonyms & Trade Names Formonitrile, Hydrocyanic acid, Prussic acid | DOT ID & Guide 1051 117 (>20% solution) 1051 117 (anhydrous) 1613 154 (</=20% solution)
Exposure Limits | NIOSH REL: ST 4.7 ppm (5 mg/m3) [skin]
OSHA PEL†: TWA 10 ppm (11 mg/m3) [skin]
IDLH 50 ppm | 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
Personal Protection & Sanitation 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
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 Escape: (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