Another look at Hydrogen Cyanide in the PEAC® Tool
We took a look at Hydrogen
Cyanide in an earlier article in July 2002, but this month we’ve decided to
take another look at this common chemical that also is very toxic. One reason
was to provide additional discussion about the substance since Dr. Nordin’s
technical discussion this month dealt with Hydrogen Cyanide exposure and its
effects that may result from fighting fires.
whose clothing or skin is contaminated with cyanide-containing solutions can
secondarily contaminate response personnel by direct contact or through
cyanide is a colorless or pale-blue liquid at room temperature. It is very
volatile, readily producing flammable and toxic concentrations at room temperature.
Hydrogen cyanide gas mixes well with air, and explosive mixtures are easily
cyanide has a distinctive bitter almond odor, but some individuals cannot
detect it and consequently, it may not provide adequate warning of hazardous concentrations.
Also the Hydrogen Cyanide odor might be masked by other odors.
cyanide is absorbed well by inhalation and can produce death within minutes.
Substantial absorption can occur through intact skin if vapor concentration is
high or with direct contact with solutions, especially at high ambient
temperatures and relative humidity. Exposure by any route may cause systemic
At temperatures below 78 °F, hydrogen cyanide is a
colorless or pale-blue liquid (hydrocyanic acid); at higher temperatures, it is
a colorless gas. Hydrogen cyanide is very volatile, producing potentially
lethal concentrations at room temperature. The vapor is flammable and
potentially explosive. Hydrogen cyanide has a faint, bitter almond odor and a
bitter, burning taste. It is soluble in water and is often used as a 96%
Hydrogen cyanide is manufactured by oxidation of
ammonia-methane mixtures under controlled conditions and by the catalytic
decomposition of formamide. It may be generated by treating cyanide salts with
acid, and it is a combustion byproduct of nitrogen-containing materials such as
wool, silk, and plastics. It is also produced by enzymatic hydrolysis of
nitriles and related chemicals. Hydrogen cyanide gas is a by-product of
coke-oven and blast-furnace operations.
Hydrogen cyanide is used in fumigating;
electroplating; mining; and in producing synthetic fibers, plastics, dyes, and
pesticides. It also is used as an intermediate in chemical syntheses.
Colorless gas or colorless or pale-blue liquid
: Almond odor at >l ppm; inadequate warning for
acute or chronic exposure
(760 mm Hg): 78 °F (25.6 °C)
: 8 °F (-13.4 °C)
0.69 (water = 1)
630 mm Hg at 68 °F (20 °C)
0.94 (air = 1)
: Miscible with water
Flammable at temperatures > 0 °F (-18 °C)
: 5.6% to 40% (concentration in air)
Hydrogen cyanide reacts with amines, oxidizers,
acids, sodium hydroxide, calcium hydroxide, sodium carbonate, caustic
substances, and ammonia. Hydrogen cyanide may polymerize at 122 °F to 140 °F.
Hydrocyanic acid, liquefied; Hydrogen cyanide, anhydrous, stabilized; Prussic
Standards and Guidelines
OSHA PEL (permissible exposure limit) (ceiling) =
10 ppm (skin) (averaged over 15 minutes)
NIOSH IDLH (immediately dangerous to life
or health) = 50 ppm
AIHA ERPG-2 (emergency response planning
guideline) (maximum airborne concentration below which it is believed that
nearly all individuals could be exposed for up to 1 hour without experiencing
or developing irreversible or other serious health effects or symptoms which
could impair an individual’s ability to take protective action) = 10 ppm.
Routes of Exposure
Hydrogen cyanide is readily absorbed from the lungs;
symptoms of poisoning begin within seconds to minutes. The odor of hydrogen
cyanide is detectable at 2–10 ppm (OSHA PEL = 10 ppm), but does not provide
adequate warning of hazardous concentrations
. Perception of the odor is a
genetic trait (20% to 40% of the general population cannot detect hydrogen
cyanide); also, rapid olfactory fatigue can occur. Hydrogen cyanide is lighter
Children exposed to the same levels of hydrogen
cyanide as adults may receive larger doses because they have greater lung
surface area:body weight ratios and increased minute volumes:weight ratios.
Skin/Eye Contact -
Exposure to hydrogen cyanide can cause skin and eye
irritation. More importantly, skin or eye absorption is rapid and contributes
to systemic poisoning. After skin exposure, onset of symptoms may be immediate
or delayed for 30 to 60 minutes. Most cases of toxicity from dermal exposure
have been from industrial accidents involving partial immersion in liquid
cyanide or cyanide solutions or from contact with molten cyanide salts,
resulting in large surface-area burns.
Children are more vulnerable to toxicants absorbed
through the skin because of their relatively larger surface area:body weight
Hydrogen cyanide is highly toxic by all routes of
exposure and may cause abrupt onset of profound CNS (Central Nervous System),
cardiovascular, and respiratory effects, leading to death within minutes.
Exposure to lower concentrations of hydrogen cyanide
may produce eye irritation, headache, confusion, nausea, and vomiting followed
in some cases by coma and death.
Hydrogen cyanide acts as a cellular asphyxiant. By
binding to mitochondrial cytochrome oxidase, it prevents the utilization of
oxygen in cellular metabolism. The CNS and myocardium are particularly
sensitive to the toxic effects of cyanide.
Acute Exposure In humans, cyanide
combines with the ferric ion in mitochondrial cytochrome oxidase, preventing
electron transport in the cytochrome system and bringing oxidative
phosphorylation and ATP production to a halt. The inhibition of oxidative
metabolism puts increased demands on anaerobic glycolysis, which results in
lactic acid production and may produce severe acid-base imbalance. The CNS is
particularly sensitive to the toxic effects of cyanide, and exposure to
hydrogen cyanide generally produces symptoms within a short period of time.Children do not always respond to chemicals in the
same way that adults do. Different protocols for managing their care may be
CNS signs and symptoms usually develop rapidly.
Initial symptoms are nonspecific and include excitement, dizziness, nausea,
vomiting, headache, and weakness. As poisoning progresses, drowsiness, tetanic
spasm, lockjaw, convulsions, hallucinations, loss of consciousness, and coma
Abnormal heartbeat can occur in cases of severe
poisoning. Slow heartbeat, intractable low blood pressure, and death may
result. High blood pressure and a rapid heartbeat may be early, transient
After systemic poisoning begins, victims may complain
of shortness of breath and chest tightness. Pulmonary findings may include
rapid breathing and increased depth of respirations. As poisoning progresses,
respirations become slow and gasping; a bluish skin color may or may not be
present. Accumulation of fluid in the lungs may develop.
Children may be more vulnerable to gas exposure
because of relatively increased minute ventilation per kg and failure to
evacuate an area promptly when exposed.
An anion-gap, metabolic acidosis occurs in severe
poisoning from increased blood levels of lactic acid. Because of their higher
metabolic rates, children may be more vulnerable to toxicants interfering with
Dermal absorption can occur, leading to systemic
toxicity. Absorption occurs more readily at high ambient temperature and
relative humidity. Because of their relatively larger surface area:body weight
ratio, children are more vulnerable to toxicants absorbed through the skin.
When splashed in the eye, hydrogen cyanide can cause
eye irritation and swelling. Eye contact with cyanide salts has produced
systemic symptoms in experimental animals.
Potential Sequelae -
Survivors of severe exposure may suffer brain damage
due to a direct action on neurons, or to lack of oxygen, or possibly due to
insufficient blood circulation. Cases of neurologic sequelae (secondary
effects) such as personality changes, memory deficits, disturbances in
voluntary muscle movements, and the appearance of involuntary movements (i.e.,
extrapyramidal syndromes) have been reported.
Chronic Exposure Chronically exposed
workers may complain of headache, eye irritation, easy fatigue, chest
discomfort, palpitations, loss of appetite, and nosebleeds. Chronic exposure
may be more serious for children because of their potential longer life span.
Hydrogen cyanide has not been classified for
carcinogenic effects, and no carcinogenic effects have been reported for
Reproductive and Developmental Effects
No reproductive or developmental
effects of hydrogen cyanide have been reported in experimental animals or
humans. Hydrogen cyanide is not included in Reproductive and Developmental
a 1991 report published by the U.S. General Accounting Office
(GAO) that lists 30 chemicals of concern because of widely acknowledged
reproductive and developmental consequences. Increased levels of thiocyanate in
the umbilical cords of fetuses whose mothers smoked compared to those whose
mothers were non-smokers suggests that thiocyanate, and possibly also cyanide,
can cross the placenta. No data were located pertaining to hydrogen cyanide in
In using the PEAC
application we access information for the chemical by first locating Hydrogen Cyanide in the database. The following figures show the screens displayed for
chemical properties, Figure 1-2 for the PEAC-WMD™ for Windows
and Figure 3-7 for the PEAC‑WMD for the Pocket PC
Figure 1 – Finding Hydrogen Cyanide in the
Figure 2 – Bottom portion of the Hydrogen Cyanide
Chemical Information Display
Review of the information
displayed in the chemical properties screen whether in Figure 1 and 2 (above)
or Figures 3-7 (below), show chemical properties values discussed earlier in
this discussion. As the reader can see, the published toxicity values, e.g.,
ERPGs (Emergency Response Planning Guidelines) published by the American
Industrial Hygiene Association and the TEELs (Temporary Emergency Exposure
Limits) published by Department of Energy are provided. We will use the ERPG-2
as the Level of Concern when we develop the Protective Action Distance (PAD) a
Figure 3- Selecting Hydrogen Cyanide using the PEAC‑WMD
for Pocket PC application
4 – Viewing the upper portion after toggling OFF the keyboard and toggling ON
Figure 5 – The NFPA 704 Hazard Classification info
Figure 6 – The Chemical and Physical Properties
Figure 7 – The published Toxicity values
The PEAC-WMD application
provides additional information and features the user can easily access by a
simple click on the screen or selection from a screen menu. As an example, the
user can toggle on the automatic Glossary feature by clicking on the Glossary
appears at the top of the screen in the Windows version of the application.
With the Glossary toggle ON, those terms that appear in the Glossary portion of
the PEAC-WMD application will appear in a different colored font on the display
as a hyperlink. If the cursor is clicked on the term, a screen will appear that
displays the definition of that term. In the example shown in Figure 8, the
Glossary icon is toggled ON and the term “ERPG-2” was clicked on. The
definition as displayed in the PEAC-WMD Glossary is shown in a separate
window. Clicking on the [OK] button on the definition window will remove the
Figure 8 – Using the interactive Glossary feature
Another benefit of using the
PEAC tool is assistance in the development of an evacuation zone for those
chemicals that produce a toxic vapor cloud. As with most of our past examples,
AristaTek creates a scenario for a spill or release of the specific chemical,
and then we work through the development of a PAD (Protective Action Distance)
to demonstrate how the PEAC system provides evacuation or exclusion zones.
For our hypothetical
scenario using Hydrogen Cyanide as the involved chemical we’ll set the location
to be plastics manufacturing facility located outside Detroit, MI. The date is January 24, about 1:30 AM with a temperature of 25°F
wind speed of 2 mph and a clear sky. The hypothetical release involves a rail
car that contains Hydrogen Cyanide and a transfer line has failed during
off-loading operations and a pool (~60 foot diameter) of Hydrogen Cyanide has
formed before the transfer line was isolated. The PEAC tool can provide
guidance with regards to toxic vapor cloud that is released.
If you decide to follow
along as we proceed through these examples, remember to set the location to Detroit and set the date and time to the proper values, otherwise you’ll compute different
values. We’ll use a terrain type of urban/forest since this is a manufacturing
facility and has buildings and processing equipment in the immediate area.
As seen at the top of the
data display screens, there is a yellow icon displayed; this is the PEAC icon
for notifying the user that a Protective Action Distance can be calculated.
Clicking or tapping on the PAD icon will display a screen as shown in Figure
9. Following through the screens, we provide information on the Meteorology,
Container Size, and Type of Release (Source). The following figures
demonstrate how we would work through our scenario to see what our Protective
Action Distance should be.
It’s Detroit in January and the temperature about
25°, wind is set for 2 mph, clear skies and the terrain is Urban/Forest since
it’s a processing facility setting.
We have selected from our list of container sizes
the Railcar selection with a default 8’ diameter and a 33’ length. This
gets us a quick estimate of how much material might be involved.
We have selected a Hole or Pipe Release, and
since the liquid boils at 78°F it will be released as a liquid and form a
pool that was specified as 60’ in diameter.
9 - Calculating a PAD using the PEAC‑WMD
By clicking the right arrow
at the top of the screen, the PEAC system will calculate a PAD based on the
default Level of Concern, which is the IDLH or 50 ppm. The PAD is calculated
to be 1.1 miles in length as shown in Figure 10.
Figure 10 – PAD based on the IDLH of 50 ppm
11 – Selecting another Level of Concern for the PAD
But perhaps we don’t want to
base the exclusion zone on the IDLH concentration; rather the decision is to
use the ERPG-2 value as defined by the AIHA (American Industrial Hygiene
Association). The definition of the ERPG-2 is “The maximum airborne
concentration below which it is believed that nearly all individuals could be
exposed for up to one hour without experiencing or developing irreversible or
other serious health effects or symptoms which could impair an individual’s
ability to take protective action.”
A new PAD can be quickly
computed by selecting the ERPG-2 value from the list of published toxicity
values as shown in Figure 11.
Instantly the PEAC-WMD
application provides a new PAD as shown in Figure 12.
12 – The PAD based on the ERGP-2 Level of Concern
When the user exits the PAD
by clicking on the [X] at the top right of the screen, a PAD
report is generated and displayed in the Data Display Field of the
PEAC-WMD application, Figure 13. The bottom of the report has the calculated
PAD graphic displayed, Figure 14. This report can be copied or printed or
recalled at a later time as needed for report development.
Figure 13 – PAD Results report generated when the
PAD Calculator is exited
Figure 14 – The PAD graphic as displayed in the PAD
Substantial portions of this
discussion were adapted from the Agency for Toxic Substances and Disease
Registry (ATSDR) Web site for Medical Management Guidelines at: http://www.atsdr.cdc.gov/