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Chemical Datasheet
HYDROCYANIC ACID, AQUEOUS SOLUTIONS, WITH MORE THAN 20% HYDROGEN CYANIDE |
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Chemical Identifiers
CAS Number |
UN/NA Number |
DOT Hazard Label |
USCG CHRIS Code |
- 74-90-8
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- Poison Inhalation Hazard
- Flammable Liquid
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none
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NIOSH Pocket Guide |
International Chem Safety Card |
Hydrogen cyanide
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- HYDROGEN CYANIDE, LIQUEFIED
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NFPA 704
General Description
Clear colorless aqueous solution of a gas. Has an odor of almonds. Can evolve hydrogen cyanide gas, which is (barely) lighter than air. Flame can flash back to the source of a gas leak very easily. Lethal doses of gas may be inhaled. Lethal doses of cyanide can be absorbed from the solution through the skin.
Hazards
Reactivity Alerts
Air & Water Reactions
No rapid reaction with air. No rapid reaction with water.
Fire Hazard
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
These materials are extremely flammable. May form explosive mixtures with air. May be ignited by heat, sparks or flames. Vapors from liquefied gas are initially heavier than air and spread along ground. Vapors may travel to source of ignition and flash back. Those substances designated with a (P) may polymerize explosively when heated or involved in a fire. Runoff may create fire or explosion hazard. Cylinders exposed to fire may vent and release toxic and flammable gas through pressure relief devices. Containers may explode when heated. Ruptured cylinders may rocket. (ERG, 2024)
Health Hazard
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
TOXIC; Extremely Hazardous. May be fatal if inhaled or absorbed through skin. Initial odor may be irritating or foul and may deaden your sense of smell. Contact with gas or liquefied gas may cause burns, severe injury and/or frostbite. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may cause environmental contamination. (ERG, 2024)
Reactivity Profile
HYDROCYANIC ACID, AQUEOUS SOLUTIONS, WITH MORE THAN 20% HYDROGEN CYANIDE react with acid to evolve hydrogen cyanide, a very poisonous colorless gas smelling of bitter almonds. Carbon dioxide from the air is sufficiently acidic to liberate HCN from aqueous solutions of hydrocyanic acid [Lewis]. The solution also can evolve gaseous hydrogen cyanide when heated. Inhalation of gaseous HCN is quickly fatal by respiratory arrest. The gas forms flammable or explosive mixtures with air (may be difficult to ignite at lower concentrations). It presents an explosion hazard when heated with or exposed to other oxidizing agents and may polymerize explosively at elevated temperature (50-60°C) or in the presence of traces of alkali [Wohler, L. et al., Chem. Ztg., 1926, 50, p. 761, 781]. Reacts violently with acetaldehyde. During the preparation of imidoester hydrochlorides, hydrogen chloride was rapidly passed over an alcoholic solution of hydrogen cyanide. An explosion ensued, despite cooling of the process [J. Org. Chem., 1955, 20, 1573].
Belongs to the Following Reactive Group(s)
- Cyanides, Inorganic
- Acids, Weak
- Polymerizable Compounds
- Water and Aqueous Solutions
Potentially Incompatible Absorbents
Use caution: Liquids with this reactive group classification have been
known to react with the
absorbents
listed below.
- Mineral-Based & Clay-Based Absorbents
- Dirt/Earth
Response Recommendations
Isolation and Evacuation
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
IMMEDIATE PRECAUTIONARY MEASURE: Isolate spill or leak area for at least 100 meters (330 feet) in all directions.
SPILL: See ERG Table 1 - Initial Isolation and Protective Action Distances on the UN/NA 1051 datasheet.
FIRE: If tank, rail tank car or highway tank is involved in a fire, ISOLATE for 1600 meters (1 mile) in all directions; also, consider initial evacuation for 1600 meters (1 mile) in all directions. (ERG, 2024)
Firefighting
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
DO NOT EXTINGUISH A LEAKING GAS FIRE UNLESS LEAK CAN BE STOPPED.
SMALL FIRE: Dry chemical, CO2, water spray or regular foam.
LARGE FIRE: Water spray, fog or regular foam. If it can be done safely, move undamaged containers away from the area around the fire. Damaged cylinders should be handled only by specialists.
FIRE INVOLVING TANKS: Fight fire from maximum distance or use unmanned master stream devices or monitor nozzles. Cool containers with flooding quantities of water until well after fire is out. Do not direct water at source of leak or safety devices; icing may occur. Withdraw immediately in case of rising sound from venting safety devices or discoloration of tank. ALWAYS stay away from tanks in direct contact with flames. (ERG, 2024)
Non-Fire Response
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
ELIMINATE all ignition sources (no smoking, flares, sparks or flames) from immediate area. All equipment used when handling the product must be grounded. Do not touch or walk through spilled material. Stop leak if you can do it without risk. Use water spray to reduce vapors or divert vapor cloud drift. Avoid allowing water runoff to contact spilled material. Do not direct water at spill or source of leak. If possible, turn leaking containers so that gas escapes rather than liquid. Prevent entry into waterways, sewers, basements or confined areas. Isolate area until gas has dispersed. Consider igniting spill or leak to eliminate toxic gas concerns. (ERG, 2024)
Protective Clothing
Excerpt from ERG Guide 117(P) [Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
Wear positive pressure self-contained breathing apparatus (SCBA). Wear chemical protective clothing that is specifically recommended by the manufacturer when there is NO RISK OF FIRE. Structural firefighters' protective clothing provides thermal protection but only limited chemical protection. (ERG, 2024)
DuPont Tychem® Suit Fabrics
Normalized Breakthrough Times (in Minutes)
Chemical |
CAS Number |
State |
QS |
QC |
SL |
C3 |
TF |
TP |
RC |
TK |
RF |
Hydrogen cyanide (21°C, liquid) |
74-90-8 |
Liquid |
|
|
|
|
|
|
135 |
>480 |
135 |
Hydrogen cyanide (27°C, gaseous) |
74-90-8 |
Vapor |
|
|
|
30 |
|
|
>480 |
>480 |
>480 |
Special Warning from DuPont: Tychem® and Tyvek® fabrics should not be
used around heat, flames, sparks or in potentially flammable or
explosive environments. Only...
(DuPont, 2024)
First Aid
Excerpt from ERG Guide 117

[Gases - Toxic - Flammable (Extreme Hazard); polymerization hazard]:
Refer to the "General First Aid" section. Specific First Aid: In case of contact with liquefied gas, only medical personnel should attempt thawing frosted parts. In case of burns, immediately cool affected skin for as long as possible with cold water. Do not remove clothing if adhering to skin. (ERG, 2024)
Physical Properties
Flash Point: data unavailable
Lower Explosive Limit (LEL): data unavailable
Upper Explosive Limit (UEL): data unavailable
Autoignition Temperature: data unavailable
Melting Point: data unavailable
Vapor Pressure: data unavailable
Vapor Density (Relative to Air): data unavailable
Specific Gravity: data unavailable
Boiling Point: data unavailable
Molecular Weight: data unavailable
Water Solubility: data unavailable
Ionization Energy/Potential:
13.60 eV
[From NPG: Hydrogen cyanide]
(NIOSH, 2024)
IDLH:
50 ppm
[From NPG: Hydrogen cyanide]
(NIOSH, 2024)
AEGLs (Acute Exposure Guideline Levels)
Final AEGLs for Hydrogen cyanide (74-90-8)
Exposure Period |
AEGL-1 |
AEGL-2 |
AEGL-3 |
10 minutes |
2.5 ppm |
17 ppm |
27 ppm |
30 minutes |
2.5 ppm |
10 ppm |
21 ppm |
60 minutes |
2 ppm |
7.1 ppm |
15 ppm |
4 hours |
1.3 ppm |
3.5 ppm |
8.6 ppm |
8 hours |
1 ppm |
2.5 ppm |
6.6 ppm |
(NAC/NRC, 2024)
ERPGs (Emergency Response Planning Guidelines)
Chemical |
ERPG-1 |
ERPG-2 |
ERPG-3 |
Hydrogen Cyanide (74-90-8)
|
NA |
10 ppm |
25 ppm |
(AIHA, 2022)
PACs (Protective Action Criteria)
Chemical |
PAC-1 |
PAC-2 |
PAC-3 |
|
Hydrogen cyanide; (Hydrocyanic acid) (74-90-8)
|
2 ppm |
7.1 ppm |
15 ppm |
LEL = 56000 ppm |
(DOE, 2024)
Regulatory Information
EPA Consolidated List of Lists
Regulatory Name |
CAS Number/ 313 Category Code |
EPCRA 302 EHS TPQ |
EPCRA 304 EHS RQ |
CERCLA RQ |
EPCRA 313 TRI |
RCRA Code |
CAA 112(r) RMP TQ |
Cyanide Compounds |
N106 |
|
|
& |
313 |
|
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Hydrocyanic acid |
74-90-8 |
100 pounds |
10 pounds |
10 pounds |
X |
P063 |
2500 pounds |
Hydrogen cyanide |
74-90-8 |
100 pounds |
10 pounds |
10 pounds |
313 |
P063 |
2500 pounds |
(EPA List of Lists, 2024)
CISA Chemical Facility Anti-Terrorism Standards (CFATS)
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RELEASE |
THEFT |
SABOTAGE |
Chemical of Interest |
CAS Number |
Min Conc |
STQ |
Security Issue |
Min Conc |
STQ |
Security Issue |
Min Conc |
STQ |
Security Issue |
Hydrocyanic acid |
74-90-8 |
1.00 % |
2500 pounds |
toxic |
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Hydrogen cyanide; [Hydrocyanic acid] |
74-90-8 |
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4.67 % |
15 pounds |
WME |
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(CISA, 2007)
OSHA Process Safety Management (PSM) Standard List
Chemical Name |
CAS Number |
Threshold Quantity (TQ) |
Hydrogen Cyanide, Anhydrous |
74-90-8 |
1000 pounds |
(OSHA, 2019)
Alternate Chemical Names
- HYDROCYANIC ACID, AQUEOUS SOLUTIONS, WITH MORE THAN 20% HYDROGEN CYANIDE