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Human beings are being exposed to toxic substances to an ever- increasing degree. The increasing
use of gases and highly volatile materials represents a danger to life.
Many gases will cause sickness, paralysis or death even when present in the atmosphere in minute concentrations.
The effects of toxic gases can be caused by skin contact, ingestion or inhalation (most common). Continuous monitoring using gas detection devices ensures that defects in installations can be
detected quickly and damage to health & property prevented.
The normal concentration of oxygen in air is 20.9%. However, it is possible for this level to be reduced during industrial operations, either because the oxygen is being consumed or absorbed or being replaced by other gases. Oxygen deficiency is a common cause of unexpected death and personnel need to be warned before the oxygen level becomes dangerously low. It is not often realised that the enrichment of oxygen in the atmosphere is also dangerous. Oxygen becomes toxic at high concentrations and the flammability of materials increases.
The two most common toxic gases encountered in industry are Carbon Monoxide (CO) and Hydrogen Sulphide (H2S). CO is a toxic, flammable, colourless & odourless gas, which is slightly lighter than air.
It is classified as a chemical asphyxiant and therefore, only small amounts of CO in the air will cause toxic reactions to occur. Excessive CO in the combustion products of oil, coal or gas boilers, furnaces or air heaters is a clear indication of incorrect or dangerous operation. Serious CO hazards are often present in situations such as vehicle maintenance workshops, multi-storey or underground carparks, road tunnels, confined spaces, coking plants, steelworks etc.
H2S is a colourless, very flammable gas, which in low concentrations has an offensive odour described as that of rotten eggs. H2S is considered a toxic gas that is extremely poisonous in very small quantities. Although it can be detected by the sense of smell in the lower ppb, sensory cells are anesthetised within 2 – 15 minutes exposure at levels > 5ppm, making it impossible to sense dangerous concentration