Hydrogen Cyanide

ATSDR • General Information 1

Hydrogen Cyanide (HCN)

CAS 74-90-8; UN 1051 

Synonyms include formonitrile. Aqueous solutions are referred to as hydrocyanic acid and prussic 

acid.

• Persons whose clothing or skin is contaminated with cyanide-containing solutions can 

secondarily contaminate response personnel by direct contact or through off-gassing 

vapor. 

• Hydrogen 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 formed. 

• Hydrogen cyanide has a distinctive bitter almond odor, but some individuals cannot 

detect it and consequently, it may not provide adequate warning of hazardous 

concentrations.

• Hydrogen 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 effects.

Description 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% aqueous solution (NIOSH 2005). 

Routes of Exposure

Inhalation 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 (20–40% of the general population 

cannot detect hydrogen cyanide); also, rapid olfactory 

fatigue can occur. Hydrogen cyanide is lighter than air 

(HSDB 2007).
Hydrogen Cyanide

2 General Information • ATSDR

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–

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 surfacearea burns (ATSDR 2006). 

Children are more vulnerable to toxicants absorbed through 

the skin because of their relatively larger surface area:body 

weight ratio.

Ingestion Ingestion of hydrogen cyanide solutions or cyanide salts 

can be rapidly fatal (ATSDR 2006). Treatment of ingested 

cyanide salts is similar to treatment of oral hydrogen 

cyanide poisoning because cyanide salts form hydrogen 

cyanide in acidic conditions. 

Sources/Uses 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 by-product 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 b y-product of coke-oven and 

blast-furnace operations (ATSDR 2006; Hartung 1994). 

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 (Hartung 1994). Hydrogen cyanide may also be 

found in cigarette smoke (ATSDR 2006; HSDB 2007).

Standards and Guidelines OSHA PEL (permissible exposure limit) (ceiling) = 10 ppm 

(skin) (averaged over 15 minutes) (OSHA 1999) 
Hydrogen Cyanide

ATSDR • General Information 3

EPA AEGL-1 (Acute Exposure Guideline Level-1) = 

2.5 ppm (10-minute) to 1 ppm (8-hour) (EPA 2007). 

Physical Properties Description: Colorless gas or colorless or pale-blue liquid 

Warning properties: Almond odor; inadequate warning 

because rapid olfactory fatigue can occur and 20–40% of 

the general population cannot smell hydrogen cyanide. 

Molecular weight: 27.03 daltons

Boiling point (760 mm Hg): 78 ΕF (25.6 °C)

Freezing point: 8 ΕF (-13.4 °C)

Specific gravity: 0.69 (water = 1)

Vapor pressure: 630 mm Hg at 68 °F (20 °C)

Gas density: 0.94 (air = 1)

Water solubility: Miscible with water

Flammability: Flammable at temperatures >0 °F (-18 °C)

Flammable range: 5.6–40% (concentration in air) (ATSDR 

2006) 

Incompatibilities Hydrogen cyanide reacts with amines, oxidizers, acids, 

sodium hydroxide, calcium hydroxide, sodium carbonate, 

caustic substances, and ammonia. Hydrogen cyanide may 

polymerize at 122–140 °F (NIOSH 2005). 
Hydrogen Cyanide

4 Health Effects • ATSDR

Health Effects

• Hydrogen cyanide is highly toxic by all routes of exposure and may cause abrupt 

onset of profound CNS, 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 (ATSDR 2006). 

Children do not always respond to chemicals in the 

same manner as adults. Different protocols for 

managing their care may be needed.

CNS 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 may occur (ATSDR 2006). 

Cardiovascular Abnormal heartbeat can occur in cases of severe 

poisoning. Slow heartbeat, intractable low blood 

pressure, and death may result. High blood pressure 

and a r apid heartbeat may be early, transient findings 

(ATSDR 2006). 
Hydrogen Cyanide

ATSDR • Health Effects 5 

Respiratory 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 

(ATSDR 2006). 

Children may be more vulnerable to gas exposure 

because of relatively increased minute ventilation per 

kg and failure to recognize the need to promptly 

evacuate an area when exposed.

Metabolic An anion-gap, metabolic acidosis occurs in severe 

poisoning from increased blood levels of lactic acid 

(ATSDR 2006). 

Because of their higher metabolic rates, children may 

be more vulnerable to toxicants interfering with basic 

metabolism.

Dermal Dermal contact with hydrogen cyanide can cause skin 

irritation (HSDB 2007).

Dermal absorption can occur, leading to systemic 

toxicity. Absorption occurs more readily at high 

ambient temperature and relative humidity (ATSDR 

2006). 

Because of their relatively larger surface area:body 

weight ratio, children are more vulnerable to toxicants 

absorbed through the skin. 

Ocular/Ophthalmic 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 (ATSDR 2006). Dilated pupils are common in 

 severe poisoning. Transient blindness can occur, although 

 it rarely does (HSDB, 2014).

 

Potential Sequelae Survivors of severe exposure may suffer brain damage 

Cases of neurologic sequelae such as personality 

changes, memory deficits, disturbances in voluntary 

muscle movements, and the appearance of involuntary 

movements (i.e., extrapyramidal syndromes) have been 

reported (ATSDR 2006). 
Hydrogen Cyanide

6 Health Effects • ATSDR

Chronic Exposure Chronically exposed workers may complain of 

headache, eye irritation, easy fatigue, chest discomfort, 

palpitations, loss of appetite, and nosebleeds (ATSDR 

2006). 

Chronic exposure may be more serious for children 

because of their potential longer life span.

Carcinogenicity Hydrogen cyanide has not been classified for 

carcinogenic effects (IARC 2007; IRIS 2007; NTP 

2005), and no carcinogenic effects have been reported 

for hydrogen cyanide. 

Reproductive and 

Developmental Effects

No hydrogen cyanide-induced developmental effects 

have been reported in humans or in animals at 

exposure levels that were not maternally toxic

(ATSDR 2006). Mild reproductive effects of sodium 

cyanide have been reported in rats and mice 

administered the substance orally for 13 weeks 

(ATSDR 2006). 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 breast milk (ATSDR 2006). 
Hydrogen Cyanide

ATSDR • Prehospital Management 7 

Prehospital Management

• A victim exposed to hydrogen cyanide gas could secondarily contaminate a 

rescuer attempting resuscitation without a respiratory barrier. Victims whose 

clothing or skin is contaminated with hydrogen cyanide liquid or solution can 

secondarily contaminate response personnel by direct contact or through offgassing vapor. Avoid dermal contact with cyanide-contaminated victims or with 

gastric contents of victims who may have ingested cyanide-containing materials. 

• Hydrogen cyanide poisoning is marked by abrupt onset of profound toxic effects 

that may include syncope, seizures, coma, gasping respirations, and 

cardiovascular collapse, causing death within minutes. These effects can occur 

from all routes of exposure.

• Victims exposed to hydrogen cyanide require supportive care and rapid 

administration of specific antidotes. 

Hot Zone Rescuers should be trained and appropriately attired 

before entering the Hot Zone. If the proper equipment 

is not available, or if rescuers have not been trained in 

its use, assistance should be obtained from a local or 

regional HAZMAT team or other properly equipped 

response organization. 

Rescuer Protection Hydrogen cyanide is a highly toxic systemic poison 

that is absorbed well by inhalation and through the 

skin. 

Respiratory Protection: Positive-pressure, selfcontained breathing apparatus (SCBA) is 

recommended in response situations that involve 

exposure to potentially unsafe levels of hydrogen 

cyanide (HSDB 2007).

Skin Protection: Chemical-protective clothing against 

hydrogen cyanide is recommended because both 

hydrogen cyanide vapor and liquid can be absorbed 

through the skin to produce systemic toxicity. 

ABC Reminders Quickly establish a patent airway, ensure adequate 

respiration and pulse. If trauma is suspected, maintain 

cervical immobilization manually and apply a cervical 

collar and a backboard when feasible.
Hydrogen Cyanide

8 Prehospital Management • ATSDR

Victim Removal If victims can walk, lead them out of the Hot Zone to 

the Decontamination Zone. Victims who are unable to 

walk may be removed on backboards or gurneys; if 

these are not available, carefully carry or drag victims 

to safety.

Victims with chemically-induced acute disorders may 

suffer from anxiety, especially children who may be 

separated from a parent or other adult.

Decontamination Zone Patients exposed only to hydrogen cyanide gas who 

have no e ye irritation do not need decontamination. 

They may be transferred immediately to the Support 

Zone. Other patients will require decontamination as 

described below.

Rescuer Protection If exposure levels are determined to be safe, 

decontamination may be conducted by personnel 

wearing a lower level of protection than that worn in 

the Hot Zone (described above). However, do not 

attempt resuscitation without a respiratory barrier.

ABC Reminders Quickly establish a patent airway, ensure adequate 

respiration and pulse. Stabilize the cervical spine with 

a collar and a backboard if trauma is suspected. 

Administer supplemental oxygen as required. Assist 

ventilation with a bag-valve-mask device if necessary.

Basic Decontamination Speed is critical. For symptomatic victims, provide 

treatment with 100% oxygen and specific antidotes as 

needed. Treatment should be given simultaneously 

with decontamination procedures. (For treatment, see

ABC Reminders, Advanced Treatment, and Antidotes 

below). 

Victims who are able may assist with their own 

decontamination. Quickly remove and double-bag 

contaminated clothing and personal belongings. 

Flush exposed skin and hair with copious amounts of 

water for at least 20 minutes. Wash with soap and rinse 

thoroughly with water. Use caution to avoid 

hypothermia when decontaminating victims,

particularly children or the elderly. Use blankets or 

warmers as needed.
Hydrogen Cyanide

ATSDR • Prehospital Management 9 

Flush exposed or irritated eyes with plain water or 

saline for 5 minutes. Remove contact lenses if easily 

removable without additional trauma to the eye. 

Continue eye irrigation during other basic care or 

transport (HSDB 2007). If pain or injury is evident, 

continue irrigation while transferring to the Support 

Zone. 

In cases of ingestion, do not induce emesis. If the 

victim is symptomatic, immediately institute 

emergency life support measures including the use 

of a cyanide antidote (see Antidotes below).

Provide reassurance to chemically-contaminated 

victims during decontamination, particularly children 

who may suffer separation anxiety if separation from a 

parent occurs. 

Transfer to Support Zone As soon as basic decontamination is complete, move 

the victim to the Support Zone.

Support Zone Be certain that victims have been decontaminated 

properly (see Decontamination Zone above). Victims 

who have undergone decontamination pose no serious 

risks of secondary contamination to rescuers. In such 

cases, Support Zone personnel require no s pecialized 

protective gear.

ABC Reminders Quickly establish a p atent airway, ensure adequate 

respiration and pulse. If trauma is suspected, maintain 

cervical immobilization manually and apply a cervical 

collar and a backboard when feasible. Administer 

supplemental oxygen as required and establish 

intravenous access if necessary. Place on a cardiac 

monitor. 

Patients who rapidly regain consciousness and who 

have no ot her signs or symptoms may not require 

antidotal treatment. Those who remain comatose or 

develop shock should be treated promptly with the 

antidotes in the cyanide antidote kit (see Antidotes 

below). 

Additional Decontamination Continue irrigating exposed skin and eyes, as 

appropriate. 
Hydrogen Cyanide

10 Prehospital Management • ATSDR

In cases of ingestion, do not induce emesis. If the 

patient is symptomatic, immediately institute 

emergency life support measures, including the use 

of a cyanide antidote (see Antidotes below).

Advanced Treatment In cases of respiratory compromise, secure airway and 

support respiration according to advanced life support 

(ALS) protocols. 

Patients who are in shock or have seizures should be 

treated according to ALS protocols. These patients or 

those who have arrhythmias may be seriously acidotic; 

consider giving, under medical supervision, 1 mEq/kg 

intravenous sodium bicarbonate (HSDB 2007).

Antidotes When possible, treatment with cyanide antidotes 

should be given under medical supervision to 

unconscious victims who have known or strongly 

suspected cyanide poisoning. There are currently two

cyanide antidotal kits approved by the U.S. Food and 

Drug Administration (FDA). Use either the standard 

cyanide antidotal kit that includes amyl nitrite perles 

and intravenous infusions of sodium nitrite and sodium 

thiosulfate or the recently approved cyanokit that 

employs intravenous infusion of hydroxocobalamin 

(FDA 2006; HSDB 2007).

Use of the standard cyanide antidotal kit includes the 

following: Amyl nitrite perles should be broken onto a 

gauze pad and held under the nose, over the Ambuvalve intake, or placed under the lip of the face mask. 

Inhale for 30 seconds every minute and use a new perle 

every 3 minutes if sodium nitrite infusions will be 

delayed (HSDB 2007). If the patient has not responded 

to oxygen and amyl nitrite treatment, infuse sodium 

nitrite intravenously as soon as possible. The usual 

adult dose is 10 mL of a 3% solution (300 mg) infused 

over absolutely no less than 5 minutes; the average 

pediatric dose is 0.12–0.33 mL/kg body weight up to 

10 mL infused as above. Monitor blood pressure 

during sodium nitrite administration, and slow the rate 

of infusion if hypotension develops (HSDB 2007).

Next, infuse sodium thiosulfate intravenously. The 

usual adult dose is 50 mL of a 25% solution (12.5 g) 

infused over 10–20 minutes; the average pediatric dose 

is 1.65 mL/kg of a 25% solution. Repeat one-half of 
Hydrogen Cyanide

ATSDR • Prehospital Management 11

the initial dose 30 minutes later if there is an 

inadequate clinical response (HSDB 2007).

Use of the Cyanokit includes the following: Infuse 

hydroxocobalamin (5 g) intravenously over 

15 minutes. Depending on the severity of poisoning 

and the clinical response, a second dose of 5 g may be 

administered over 15 minutes to 2 hours (based on 

patient condition). The recommended diluent is 0.9% 

sodium chloride. Some drugs are incompatible with 

hydroxocobalamin, in which case, a separate 

intravenous line may be necessary (Drugs.com 2007). 

Transport to Medical Facility Only decontaminated patients or patients not requiring 

decontamination should be transported to a medical 

facility. “Body bags” are not recommended.

Report to the base station and the receiving medical 

facility the condition of the patient, treatment given, 

and estimated time of arrival at the medical facility.

If a cyanide-containing solution has been ingested, 

prepare the ambulance in case the victim vomits. Have 

ready several towels and open plastic bags to quickly 

clean up and isolate vomitus.

Multi-Casualty Triage Consult with the base station physician or the regional 

poison control center for advice regarding triage of 

multiple victims. 

Patients with evidence of significant hydrogen cyanide 

exposure, and all patients with oral exposure to

hydrogen cyanide and those with potentially hazardous 

dermal exposure, should be transported to a medical 

facility for evaluation.

Patients who have only brief inhalation exposure and 

mild or transient symptoms may be discharged from 

the scene after their names, addresses, and telephone 

numbers are recorded. They should be advised to seek 

medical care promptly if symptoms develop or recur 

(see Patient Information Sheet below). 
Hydrogen Cyanide

12 Emergency Department Management • ATSDR

Emergency Department Management

• Hospital personnel in an enclosed area can be secondarily contaminated by 

vapor off-gassing from heavily soaked clothing or skin, or from vomitus. Avoid 

dermal contact with cyanide-contaminated patients or with gastric contents of 

patients who may have ingested cyanide-containing materials. Patients do not 

pose secondary contamination risks after contaminated clothing is removed and 

the skin is washed.

• Hydrogen cyanide poisoning is marked by abrupt onset of profound health

effects that may include syncope, seizures, coma, gasping respirations, and 

cardiovascular collapse, causing death within minutes. 

• Patients exposed to hydrogen cyanide can survive with supportive care and 

rapid administration of specific antidotes.

Decontamination Area Previously decontaminated patients and patients 

exposed only to hydrogen cyanide gas and have no 

skin or eye irritation may be transferred immediately to 

the Critical Care Area. Other patients require 

decontamination as described below. 

ED personnel should don butyl rubber gloves and 

aprons before treating patients who have been exposed 

to hydrogen cyanide liquid or solutions. Hydrogen 

cyanide readily penetrates most rubbers and barrier 

fabrics or creams, but butyl rubber provides good skin 

protection for a short period of time. 

Be aware that use of protective equipment by the 

provider may cause anxiety, particularly in children, 

resulting in decreased compliance with further 

management efforts.

Because of their relatively larger surface area:body 

weight ratio, children are more vulnerable to toxicants 

absorbed through the skin. 

ABC Reminders Evaluate and support airway, breathing, and circulation

according to ALS protocols. 

Patients who are comatose, hypotensive, or have 

seizures or cardiac dysrhythmias should be treated in 

the conventional manner. If not previously 
Hydrogen Cyanide

administered, give sodium bicarbonate intravenously to 

these patients (HSDB 2007). Further bicarbonate 

therapy should be guided by ABG measurements. 

Basic Decontamination Patients who are able may assist with their own 

decontamination. Remove and double-bag 

contaminated clothing and personal belongings. 

Speed is critical. If the patient is symptomatic, 

immediately institute emergency life support 

measures, including the use of a cyanide antidote kit

(see Antidotes in the Prehospital Management 

section above).

If the patient’s clothing is wet with hydrogen cyanide 

solution, quickly remove contaminated clothing while 

flushing exposed skin and hair with plain water for 2–

3 minutes (preferably under a shower), then wash twice 

with mild soap (HSDB 2007). Use caution to avoid 

hypothermia when decontaminating victims, 

particularly children or the elderly. Use blankets or 

warmers as needed.

Irrigate exposed eyes for at least 5 minutes. Remove 

contact lenses if easily removable without additional 

trauma to the eye. Continue irrigation while 

transporting the patient to the Critical Care Area.

In cases of ingestion, do not induce emesis. If the 

victim is alert, asymptomatic, and has a gag reflex, 

consider administering a slurry of activated charcoal at 

a dose of 1 g/kg (infant, child, and adult dose) (HSDB 

2007). Because cyanide absorption from the gut is 

rapid, the effectiveness of activated charcoal will 

depend on how quickly after ingestion it can be 

administered. Consider gastric lavage if the patient is 

conscious and it can be performed shortly after 

ingestion. Isolate gastric washings and vomitus; they 

may off-gas hydrogen cyanide (HSDB 2007).

Critical Care Area Be certain that appropriate decontamination has been 

carried out (see Decontamination Area above). 

ATSDR • Emergency Department Management 13
Hydrogen Cyanide

14 Emergency Department Management • ATSDR

ABC Reminders Evaluate and support airway, breathing, and circulation 

as in ABC Reminders above under Decontamination 

Zone. Establish intravenous access in seriously ill 

patients if this has not been done previously. 

Continuously monitor cardiac rhythm. 

Patients who are in shock or have seizures should be 

treated according to ALS protocols. These patients or 

those who have dysrhythmias may be seriously 

acidotic; consider giving 1 mEq/kg intravenous sodium 

bicarbonate (HSDB 2007).

Inhalation Exposure Inhalation is the primary route of exposure to hydrogen 

cyanide. Refer to Antidotes and Other Treatments 

below for appropriate clinical treatment of systemic 

effects.

Skin Exposure If the skin contacted hydrogen cyanide liquid or 

cyanide solutions, chemical burns may occur; treat as 

thermal burns. Watch for signs or symptoms of 

systemic toxicity, which may be delayed in onset for 

up to 1 hour. 

Eye Exposure Continue irrigation for at least 15 minutes. Test visual 

acuity. Examine the eyes for corneal damage and treat 

appropriately. Immediately consult an ophthalmologist 

for patients who have corneal injuries. 

Ingestion Exposure Do not induce emesis. If the victim is symptomatic, 

immediately institute emergency life support 

measures including the use of a cyanide antidote kit 

(see Antidotes in the Prehospital Management 

section above). If the victim is alert, asymptomatic, 

has a gag reflex, and it has not been done previously, 

consider performing gastric lavage. 

Vomitus or gastric washings should be isolated (e.g., 

by attaching the lavage tube to isolated wall suction or 

another closed container). 
Hydrogen Cyanide

ATSDR • Emergency Department Management 15

Antidotes and Other Treatments Patients who have signs or symptoms of significant 

systemic toxicity should be evaluated for antidotal 

treatment. There are currently two cyanide antidotal 

kits approved by the U.S. FDA. Use either the cyanide 

antidotal kit that includes amyl nitrite perles and 

intravenous infusions of sodium nitrite and sodium 

thiosulfate or the recently approved cyanokit that 

employs intravenous infusion of hydroxocobalamin 

(FDA 2006; HSDB 2007). For instructions on us e of 

cyanide antidotal kits, see Antidotes in the Prehospital 

Management section above. 

The efficacy of hyperbaric oxygen in cyanide 

poisoning is unproven. It has been reported to be useful 

in severe cases of smoke inhalation combined with 

exposure to hydrogen cyanide and carbon monoxide 

(HSDB 2007).

Laboratory Tests The diagnosis of acute cyanide toxicity is primarily a 

clinical one (based on rapid onset of CNS toxicity and 

cardiorespiratory collapse). Specific tests for the 

presence of cyanide in blood and urine may be useful 

in confirming exposure, but have limited usefulness in 

acute treatment decisions. Routine laboratory studies 

for all exposed patients include CBC, blood glucose, 

and electrolyte determinations. Additional studies for 

patients exposed to hydrogen cyanide include ECG

monitoring, determinations of serum lactate and 

urinary thiocyanate, chest radiography, and pulse 

oximetry (or ABG measurements) (Hall and Rumack 

1998). Some pulse oximeters may give spurious results 

in the presence of hemoglobin species other than 

oxyhemoglobin and deoxyhemoglobin. 

In severe poisonings, venous blood is oxygenated and 

has a bright red color. Elevated venous PO2 and 

venous percent O2 saturation occurs, narrowing the 

gap between arterial and central venous PO2 or percent 

O2 saturation (Hall and Rumack 1998). 

After treatment with nitrites, serum methemoglobin 

levels may be monitored. Whole blood cyanide tests 

generally require several hours and cannot be used to 

guide emergency treatment. However, blood cyanide 

levels may be useful in documenting exposure (Hall 

and Rumack 1998; Kruszyna et al. 1993). 
Hydrogen Cyanide

16 Emergency Department Management • ATSDR

MRI studies may be useful in identifying the location 

and extent of brain injury in patients with cyanideinduced Parkinsonian syndrome. 

Disposition and Follow-up Consider hospitalizing patients who have histories of 

significant exposure and are symptomatic. Whenever 

infusions from a cyanide antidote kit are used, the 

patient should be admitted to the intensive care unit 

(Hall and Rumack 1998). 

Delayed Effects Patients who have ingested hydrogen cyanide solutions 

or patients who have direct skin or eye contact should 

be observed in the Emergency Department for at least 

4 to 6 hours (Hall and Rumack 1998). 

Patient Release Patients who remain asymptomatic 4 to 6 hours after 

exposure may be discharged with instructions to seek 

medical care promptly if symptoms develop (see the 

Hydrogen Cyanide—Patient Information Sheet below). 

Follow-up Obtain the name of the patient’s primary care 

physician so that the hospital can send a copy of the 

ED visit to the patient’s doctor.

Survivors of a serious exposure should be evaluated for 

ischemic damage to the brain and heart. Patients who 

have serious systemic cyanide poisoning may be at risk 

for CNS sequelae including Parkinsonian-like 

syndromes; they should be monitored for several 

weeks to months (Hall and Rumack 1998). 

Patients who have corneal injuries should be 

reexamined within 24 hours. 

Reporting If a work-related incident has occurred, you may be 

legally required to file a report; contact your state or 

local health department.

Other persons may still be at risk in the setting where 

this incident occurred. If the incident occurred in the 

workplace, discussing it with company personnel may 

prevent future incidents. If a public health risk exists, 

notify your state or local health department or other 

public agency. When appropriate, inform patients that 

they may request an evaluation of their workplace from 
Hydrogen Cyanide

ATSDR • Emergency Department Management 17

OSHA or NIOSH. See Appendices III and IV for a list 

of agencies that may be of assistance.
Hydrogen Cyanide

18 Patient Information Sheet • ATSDR

Hydrogen Cyanide

Patient Information Sheet

This handout provides information and follow-up instructions for persons who have been exposed 

to hydrogen cyanide. 

What is hydrogen cyanide?

At room temperature, hydrogen cyanide is a volatile, colorless-to-blue liquid (also called 

hydrocyanic acid). It rapidly becomes a gas that can produce death in minutes if breathed. Hydrogen 

cyanide is used in making fibers, plastics, dyes, pesticides, and other chemicals, and as a fumigant 

to kill rats. It is also used in electroplating metals and in developing photographic film. Low 

cyanide levels can be measured in cigarette smoke.

What immediate health effects can be caused by exposure to hydrogen cyanide?

Breathing small amounts of hydrogen cyanide may cause headache, dizziness, weakness, nausea, 

and vomiting. Larger amounts may cause gasping, irregular heartbeats, seizures, fainting, and even 

rapid death. Generally, the more serious the exposure, the more severe the symptoms. Similar 

symptoms may be produced when solutions of hydrogen cyanide are ingested or come in contact 

with the skin. 

Can hydrogen cyanide poisoning be treated?

The treatment for cyanide poisoning includes breathing pure oxygen, and in the case of serious 

symptoms, treatment with specific cyanide antidotes. Persons with serious symptoms will need to 

be hospitalized. 

Are any future health effects likely to occur?

A single small exposure from which a person recovers quickly is not likely to cause delayed or 

long-term effects. After a serious exposure, a patient may have brain or heart damage.

What tests can be done if a person has been exposed to hydrogen cyanide?

Specific tests for the presence of cyanide in blood and urine may be useful in confirming exposure, 

but have limited usefulness in acute treatment decisions. If a severe exposure has occurred, blood 

and urine analyses and other tests may show whether the brain or heart has been injured. Testing is 

not needed in every case.

Where can more information about hydrogen cyanide be found?

More information about hydrogen cyanide can be obtained from your regional poison control

center; your state, county, or local health department; the Agency for Toxic Substances and Disease 

Registry (ATSDR); your doctor; or a clinic in your area that specializes in occupational and 

environmental health. If the exposure happened at work, you may wish to discuss it w ith your 

employer, the Occupational Safety and Health Administration (OSHA), or the National Institute for 

Occupational Safety and Health (NIOSH). Ask the person who gave you this form for help in 

locating these telephone numbers. 
Hydrogen Cyanide

ATSDR • Patient Information Sheet 19

Follow-up Instructions

Keep this page and take it with you to your next appointment. Follow only the instructions checked 

below. 

[ ] Call your doctor or the Emergency Department if you develop any unusual signs or symptoms 

within the next 24 hours, especially: 

• difficulty breathing, shortness of breath, or chest pain 

• confusion or fainting 

• increased pain or a discharge from your eyes

• increased redness, pain, or a pus-like discharge in the area of a skin burn 

[ ] No follow-up appointment is necessary unless you develop any of the symptoms listed above. 

[ ] Call for an appointment with Dr. ______________ in the practice of ______________________. 

When you call for your appointment, please say that you were treated in the Emergency Department 

at _______________ Hospital by _____________________________ and were advised to be seen 

again in __________ days. 

[ ] Return to the Emergency Department/_______________ Clinic on (date) _______________ at 

_________________________ AM/PM for a follow-up examination. 

[ ] Do not perform vigorous physical activities for 1 to 2 days. 

[ ] You may resume everyday activities including driving and operating machinery. 

[ ] Do not return to work for _____ days.

[ ] You may return to work on a limited basis. See instructions below. 

[ ] Avoid exposure to cigarette smoke for 72 hours; smoke may worsen the condition of your lungs. 

[ ] Avoid drinking alcoholic beverages for at least 24 hours; alcohol may worsen injury to your 

stomach or have other effects.

[ ] Avoid taking the following medications: _____________________________________________ 

[ ] You may continue taking the following medication(s) that your doctor(s) prescribed for you: 

________________________________________________________________________________ 

________________________________________________________________________________ 

[ ] Other instructions: ______________________________________________________________ 

________________________________________________________________________________ 

________________________________________________________________________________ 

• Provide the Emergency Department with the name and the number of your primary care 

physician so that the ED can send him or her a record of your emergency department visit. 

• You or your physician can get more information on t he chemical by contacting: 

____________________________or _______________________, or by checking out the 

following Internet Web sites: ________________________________________________; 

____________________________________________________________________________. 

Signature of patient ________________________________ Date ___________________________ 

Signature of physician ______________________________ Date ___________________________ 
Hydrogen Cyanide

20 References • ATSDR

References

AIHA. 1994. Emergency response planning guidelines: Hydrogen cyanide. Fairfax, VA: American 

Industrial Hygiene Association. 

ATSDR. 2006. Toxicological profile for cyanide (update). U.S. Department of Health and Human 

Services. Agency for Toxic Substances and Disease Registry.

Drugs.com. 2007. Drug information online: Cyanokit injection. 

http://www.drugs.com/pro/cyanokit.html. October 11, 2007. 

EPA. 2007. Hydrogen cyanide results. Acute Exposure Guideline Levels (AEGLs). U.S. 

Environmental Protection Agency. http://www.epa.gov/opptintr/aegl/pubs/results6.htm. January 12, 

2007. 

FDA. 2006. FDA news: FDA approves drug to treat cyanide poisoning. U.S. Food and Drug 

Administration. http://www.fda.gov/bbs/topics/NEWS/2006/NEW01531.html. October 11, 2007. 

Hall AH, Rumack BH. 1998. Cyanide and related compounds. In: Haddad LM, Winchester JF, eds. 

Clinical management of poisoning and drug overdose. 2nd ed. Philadelphia, PA: W.B. Saunders 

Company, 899-905. 

Hartung R. 1994. Cyanides and nitriles. In: Clayton GD, Clayton FE, ed. Patty's industrial hygiene 

and toxicology. New York, NY: John Wiley & Sons, Inc., 3119-3127. 

HSDB. 2007. Hydrogen cyanide. Hazardous Substances Data Bank. National Library of Medicine. 

http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB. October 11, 2007. 

IARC. 2007. International Agency for Research on Cancer. 

http://monographs.iarc.fr/ENG/Classification/Listagentsalphorder.pdf. October 11, 2007. 

IRIS. 2007. Hydrogen cyanide. Integrated Risk Information System. U.S. Environmental Protection 

Agency. http://www.epa.gov/iris/subst/0060.htm. October 11, 2007. 

Kruszyna R, Kruszyna HG, Smith RP. 1993. A spectrophotometric method for estimating 

methemoglobin concentration in the presence of cyanide. Am J Emerg Med 11(6):642-643. 

NIOSH. 2005. Hydrogen cyanide. NIOSH pocket guide to chemical hazards. National Institute for 

Occupational Safety and Health. http://www.cdc.gov/niosh/npg/npgd0333.html. October 11, 2007. 

NTP. 2005. Report on carcinogens. 11th ed. National Toxicological Program. National Institute of 

Environmental Health Sciences. http://ntp.niehs.nih.gov/ntpweb/index.cfm?objectid=035E5806-

F735-FE81-FF769DFE5509AF0A. October 11, 2007. 
Hydrogen Cyanide

ATSDR • References 21

OSHA. 1999. Hydrogen cyanide. U.S. Department of Labor. Occupational Safety and Health 

Administration. Code of Federal Regulations. 29 CFR 1910.1000. TableZ-1. Part Z, Toxic and 

Hazardous Substances. 

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9992. 

October 11, 2007.