Diseases Caused by Asphyxiants: Carbon Monoxide and Hydrogen Cyanide

1. Introduction and Definitions

Asphyxiants are substances that can cause unconsciousness or death by suffocation. They work by displacing oxygen in the air or by interfering with the body's ability to use oxygen. Two of the most common and dangerous asphyxiants in occupational settings are carbon monoxide (CO) and hydrogen cyanide (HCN). Exposure to these gases can lead to severe health issues and even fatalities. This article aims to provide comprehensive information on diseases caused by asphyxiants like carbon monoxide and hydrogen cyanide, targeting occupational health nurses and doctors.

2. Agent Causes the Disease

Carbon Monoxide (CO):

  • Properties: CO is a colorless, odorless gas that results from the incomplete combustion of carbon-containing materials.
  • Mechanism: CO binds to hemoglobin in the blood, forming carboxyhemoglobin (COHb), which reduces the blood's oxygen-carrying capacity and impairs oxygen delivery to tissues.

Hydrogen Cyanide (HCN):

  • Properties: HCN is a colorless or pale blue liquid or gas with a bitter almond odor, produced by the combustion of nitrogen-containing substances.
  • Mechanism: HCN interferes with cellular respiration by inhibiting cytochrome c oxidase, an enzyme essential for the electron transport chain in mitochondria, preventing cells from utilizing oxygen.

3. Workers at Risk of This Disease

Several occupations and tasks put workers at higher risk of exposure to asphyxiants like carbon monoxide and hydrogen cyanide, including:

  • Firefighters: Exposure to CO and HCN from combustion products during firefighting.
  • Industrial Workers: Working in industries with high-temperature processes, such as steel production, where CO is a byproduct.
  • Chemical Plant Workers: Handling or producing chemicals that can release HCN.
  • Motor Vehicle Mechanics: Exposure to CO from engine exhaust in poorly ventilated areas.
  • Agricultural Workers: Exposure to CO from equipment engines or HCN from fumigants and pesticides.
  • Miners: Exposure to CO from explosives and machinery.

4. Symptoms

Symptoms of exposure to asphyxiants can vary depending on the concentration and duration of exposure:

Carbon Monoxide (CO) Exposure:

  • Low to Moderate Exposure: Symptoms include headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion.
  • High Exposure: Symptoms can escalate to loss of consciousness, seizures, and death due to hypoxia.

Hydrogen Cyanide (HCN) Exposure:

  • Acute Exposure: Symptoms include headache, dizziness, shortness of breath, chest pain, nausea, and vomiting. Severe exposure can cause loss of consciousness, seizures, cardiac arrest, and death.
  • Chronic Exposure: Symptoms include weakness, headaches, vertigo, and symptoms of neurotoxicity.

5. Diagnosis

Diagnosing diseases caused by asphyxiants involves a combination of clinical evaluation, occupational exposure assessment, and specific tests:

  • Medical History and Physical Examination: Detailed assessment of the patient's work history and symptoms.
  • Blood Tests:
    • For CO exposure: Measuring carboxyhemoglobin (COHb) levels.
    • For HCN exposure: Measuring blood cyanide levels or using methemoglobin levels as an indirect indicator.
  • Pulse Oximetry and CO-Oximetry: Non-invasive methods to assess blood oxygen levels and COHb.
  • Neurological Evaluation: Assessing cognitive and motor functions if neurological symptoms are present.

6. Treatment

Treatment for diseases caused by asphyxiants focuses on removing the patient from exposure, providing supportive care, and administering specific antidotes:

Carbon Monoxide (CO) Exposure:

  • Remove from Exposure: Immediate removal from the source of CO and providing fresh air.
  • Oxygen Therapy: Administering 100% oxygen via non-rebreather mask or hyperbaric oxygen therapy to enhance the elimination of CO from the blood.
  • Supportive Care: Monitoring and supporting cardiovascular and neurological functions.

Hydrogen Cyanide (HCN) Exposure:

  • Remove from Exposure: Immediate removal from the source of HCN and providing fresh air.
  • Antidotes: Administering specific antidotes such as hydroxocobalamin or sodium thiosulfate.
  • Oxygen Therapy: Providing supplemental oxygen to support cellular respiration.
  • Supportive Care: Monitoring and supporting cardiovascular and neurological functions.

7. Prevention

Preventing diseases caused by asphyxiants involves implementing strict control measures in the workplace:

  • Engineering Controls: Using ventilation systems, gas detectors, and alarms to monitor and reduce levels of CO and HCN in the air.
  • Work Practices: Implementing safe work practices such as proper handling and disposal of chemicals, regular maintenance of equipment, and ensuring adequate ventilation in work areas.
  • Personal Protective Equipment (PPE): Providing and ensuring the use of appropriate respirators and protective clothing.
  • Health Surveillance: Regular health screenings, including blood tests for workers exposed to asphyxiants.
  • Education and Training: Informing workers about the hazards of CO and HCN and safe work practices to minimize exposure.

By recognizing the hazards of asphyxiants like carbon monoxide and hydrogen cyanide and applying effective preventive strategies, occupational health professionals can substantially lower the occurrence of related illnesses and improve the overall health and safety of workers.

Workplace Exposure Limits:

Hydrogen Cyanide

  • OSHA: The legal airborne permissible exposure limit (PEL) is 10 ppm averaged over an 8-hour workshift. 
  • NIOSH: The recommended airborne exposure limit (REL) is 4.7 ppm

Carbon Monoxide

  • OSHA: The legal airborne permissible exposure limit (PEL) is 50 ppm averaged over an 8-hour workshift.
  • NIOSH: The recommended airborne exposure limit (REL) is 35 ppm averaged over a 10-hour workshift and 200 ppm, not to be exceeded during any 15-minute work period.