Asphyxiant agents

Asphyxiant agents cause hypoxia in the tissues following inhalation without causing damage to the lung structures. They may be divided into the following  

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Chemical asphyxiants (agents blocking cellular respiration) Hydrogen cyanide, cyanogen chloride and bromide... 

Muscle twitching and excess secretions are the main distinguishing features between nerve agents and chemical asphyxiant agents, such as cyanide. 

Phosphine is another chemical asphyxiant agent worthy of mention. This is a colourless and flammable gas, exposure to which causes inhibition of cytochrome C oxidase and mitochondrial oxygen uptake. Symptoms usually occur within the first few hours of exposure. Treatment is essentially the same as that for arsine, relying on supportive measures. 

LPG is considered to be non-toxic witli no chronic effects, but the vapour is slightly anaesthetic. In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physical asphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g. methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell down to approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorant is not added for specific applications, e.g. cosmetic aerosol propellant. 

After skin is exposed to HN-2 an epidermal rash develops within approximately an hour. If initial exposure is very low, a rash may not develop. As with HN-1, HN-2 exposure is cumulative. If a person receives multiple low-level exposures, a rash will eventually appear. Blistering will begin about 12 hours after the onset of the skin rash. As with other blister agents, great irritation results when HN-2 vapor or liquid mixes with sweat and flows to tender skin areas (e.g., armpits, buttocks, crotch). Pulmonary effects from exposure to HN-2 are not as severe as for distilled mustard. Dry-land drowning syndrome can occur as the lungs flood with mucus, dead tissue, and blood. The victim dies from a combination of asphyxiation and heart failure. 

Carbon dioxide (CO2) is a colorless and odorless gas. It is an asphyxiant-causing agent. A concentration of 10% can cause unconsciousness and death from oxygen deficiency. The gas can be released from industrial studies [39], automobile exhaust, environmental tobacco smoke (ETS), and inadequately vented fuel heating systems. It is heavy and accumulates at low levels in depressions and along the floor. 

To a large extent, therefore, the toxicities of esters tend to be those of their hydrolysis products. Two physical characteristics of many esters that affect their toxicities are relatively high volatility, which promotes exposure by the pulmonary route, and good solvent action, which affects penetration and tends to dissolve body lipids. Many volatile esters exhibit asphyxiant and narcotic action. As expected for compounds that occur naturally in foods, some esters are nontoxic (in reasonable doses). However, some of the synthetic esters, such as allyl acetate, have relatively high toxicities. As an example of a specific toxic effect, vinyl acetate acts as a skin defatting agent. 

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