Some gases and vapours have a sharp or irritating smell. This smell is an early warning signal. The gases which do not give a warning signal or which rapidly reduce our ability to realise or assess the danger are even more dangerous. Gases may spread into the workplace air through various chemical processes or through leakage from gas cylinders.
There are two types of gases
- Irritant gases, which have a corrosive or irritating effect on the breathing organs;
- Gases which are absorbed by the blood and affect the internal organs.
Chlorine and sulphur dioxide are examples of irritant gases. A high concentration of these in the air can damage the lungs. Other irritant gases are phosgene and the nitrous gases. They do not provide a warning signal in the form of irritation when breathing. Phosgene is formed when e.g. trichloroethylene or tetrachloroethylene come into contact with hot surfaces or naked flames. Nitrous gases are formed when the oxygen and nitrogen in the air are heated intensely, as in welding.
Some gases which can affect the internal organs are carbon monoxide, hydrogen sulphide and radon. Carbon monoxide is a colourless and odourless gas which combines with the oxygen-carrying elements of our blood faster than oxygen can. Exposures to certain levels of carbon monoxide may result in acute medical conditions and death.
A word of caution is necessary about the lack of oxygen that can occur in confined spaces (silos, tanks, reaction vessels, air-tight compartments, etc.). This is a very dangerous situation and can rapidly kill. Oxygen may be removed from the air by, e.g. excessive carbon dioxide due to fermentation, slow oxidation during rusting, etc. Setting up and enforcing proper procedures are absolutely necessary for working in confined spaces.