The New Straits Times, October 23, 1995
Q: What affects can someone experience in gas exposure?
A: Inhalation represents one of the most important routes of poisoning. This is because the lungs, by virtue of their large surface area and good blood supply, provide an excellent route for absorption and distribution.
Inhalation of some gases can cause irritation and injury to the lungs, while others may even cause significant systemic poisoning involving vital organs such as the brain, kidney and liver. Gases can be classified based on their nature of toxic action:
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Irritants - Examples: ammonia, chlorine, sulphur dioxide, ozone, phosgene, halogens, acrolein.
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Simple asphyxiants - Nitrogen, hydrogen, methane, helium, propane.
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Chemical asphyxiants - Carbon monoxide, hydrogen, cyanide, nitrites, hydrogen sulphides.
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Central nervous system depressants - aliphatic hydrocarbons, chlorinated hydrocarbons, acetone, ethyl ether, benzene
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Neurotoxic agents - Carbon disulphide, mercury, acrylamide, n-hexane, methyl n-butyl ketone.
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Hepatotoxic agents - Carbon tetrachloride, chloroform, allyl alcohol, bromobenzene.
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Nephorothoxic agents - Carbon tetrachloride, chloroform, trichloroethylene.
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Agents damaging blood - Nitrobenzene, arsine, naphthalene.
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Agents damaging bone marrow - Benzene, trinitrotoluene.
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Carcinogens - vinyl chloride, 2-naphthylamine, bis(chloromethyl)ether.
Two commonly-encounered groups of gases belong to the asphyxiants and irritants. Simple asphyxiants are physiolocigal inert. When They are present in high concentration, they displace the oxygen in the atmosphere. Victims exposed to them will suffer from lack of oxygen. Carbon dioxide and methane are classic examples of simple asphyxiant.
Chemical asphyxiants, on the other hand, interfere with the body's ability to utilise oxygen, They either prevent oxygen delivery (such as carbon monoxide and hydrogen sulphide) or inhibit the utilisation of oxygen by the cells. Both types of asphyxiants however produce, if any, minimal direct injury to the respiratory system though they can cause marked neurologic and metabolic alterations.
Irritants have the ability to cause injury and induce inflammation of the mucous membranes upon contact. Individuals exposed to these gases may develop signs and symptoms either predominantly associated with upper or lower respiratory tract involvement. This depends very much on the solubility of the gas. Highly water-soluble gases like ammonia affect mainly the upper respiratory tract, while low water-soluble gases like phosgene affect the lower respiratory tract.
Generally, irritation of the upper respiratory tract may cause rhinitis, pharyngitis, cough and laryngeal edema while irritation of the lower respiratory tract may cause pneumonitis, pulmonary edema, and shock.
Signs of lower respiratory tract involvement may not necessarily be preceded by involvement of the upper respiratory tract. However, injury to the upper respiratory tract may be extended to involve the lower respiratory tract if exposure is prolonged. This seems to be the standard for gases with intermediate water solubility.
Irritants can be classified into two groups. They are the primary irritants that produce little systemic toxicity and secondary irritants that produce both respiratory and toxic systemic toxicity. Toxic substances that are classified under secondary irritants include hydrogen sulfide, ozone acetylene, methylated halogens, and metal fumes.
Individuals exposed to these substances may, however, experience varied effects. The nature, extent and severity of the effects observed may depend among other things on the types of gas involved, solubility, concentration as well as the extent and duration of exposure. Poorly-ventilated exposure sites will very likely cause more significant effects and so with individuals who have pre-existing lung diseases.
