Module 3: Toxicology - Section 10: Toxic Gases

TOX 10.2: General Characteristics of Toxic Gases

IMPORTANT GENERAL CHARACTERISTICS OF HAZARDOUS GASES:

1. Mechanism of injury varies:

   • Physical ("simple") asphyxiants:
     Replace oxygen, typically in a confined space, e.g. carbon dioxide, methane, acetylene;
     
   • Chemical asphyxiants:
     Chemically interfere with respiration, e.g. carbon monoxide, cyanide, hydrogen sulphide;
     
   • Irritant:
     Strongly acidic, alkaline, corrosive so that it damages surfaces , e.g. chlorine, ammonia;
     • Lower respiratory tract: Bronchitis, bronchiolitis, alveloitis, Adult Respiratory Distress Syndrome, pulmonary oedema (See below);
       
   • Multisystem toxin: (e.g. CNS, kidney, blood), e.g. arsine, phosphine.
   
   

2. Solubility = primary determinant of harm:

   • High solubility: ammonia, hydrogen chloride - impact mostly in upper respiratory tract;
   • Moderate solubility: sulphur dioxide, chlorine - in between;
   • Low solubility: ozone, oxides of nitrogen - impact deeper in lung.
   
   

3. Timing and severity of effects vary:

   (Almost all affect the respiratory system)
   
   • Acute: immediate illness, or within hours.
   • Delayed onset: The first symptoms may occur hours even days after the exposure. This may obscure the association of cause and effect.
   • Post-acute: Recovers from acute illness, but late and persistent symptoms occur.
   • Chronic effects with persistent low dose - appears after years of exposure.
   
   

4. Olfactory fatigue is an important determinant of hazard:

   Ability to detect the gas by smell, which can act as a warning, wanes over the course of the shift. Usually recovers for next shift.

5. Occult exposure may occur:

   Odourless gases are particularly dangerous. Exposure may not even be detected!

6. Individuals vary in their susceptibility to harm:

   Asthmatics, COPD sufferers and those with cardiovascular disease are particularly vulnerable

7. Clinical Monitoring (of respiratory effects) (generic)

   Symptoms, adventitous sounds, spirometry, Pa02, oxygen saturation ( %), CXR changes (subtle).

8. Treatment (generic):

   • Supportive; expectant!
   • Maintain airway; 100% 0₂ (?hyperbaric); Intensive care, Positive pressure ventilation.
   • IV steroids, bronchodilators.
   • Antidotes (if relevant).
   • Follow-up.
     
     

9. Controls and prevention:

   • Enclosure/separation of gases
   • Extraction of emissions
   • Early warning systems
   • Training of workers in recognition, response and evasion
   • Buddy system for tanks
   • Decontamination/evacuation procedures in case of emergency/leak/spill
   • PPE (+ Self contained breathing apparatus)
   
   

Glossary of lung injury:

Bronchitis: Inflammation of the bronchial tree
Bronchiolitis: Inflammation of the bronchioles, i.e. the smallest branches of the bronchial tree
Alveolitis: Inflammation of the gas exchange part of the lung
Pulmonary oedema: Filling of the gas exchange part of the lung with fluid. Occurs with lung injury but also in heart failure
Adult Respiratory Distress Syndrome (ARDS): diffuse parenchymal lung injury resulting in severe respiratory distress and hypoxaemic respiratory failure.
Emphysema: Breakdown of the gas exchange part of the lungs including the respiratory bronchioles, so that the alveoli are replaced with non-functional "holes".

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
Disclaimer note: Some resources and descriptions may be out-dated. For suggested updates and feedback, please contact healthoer@uct.ac.za.