Toxic gases are substances in the gaseous state that cause hazardous physiological effects when inhaled, affecting the respiratory, cardiovascular, and nervous systems, making them major public hazards (WHO 2000).
Ammonia (NH3) is a colourless acrid-smelling reactive gas at ambient temperature and pressure and is considered a significant public health hazard (WHO, 1986; PHE, 2019).
Chlorine is a reactive pale green gas with many uses including disinfection of water. Chlorine is approximately 2.4 times heavier than air and has a characteristic odour similar to bleach. Most significant exposures to chlorine result from loss of containment of chlorine during storage and transport. Human exposure can result in symptoms ranging from mild irritation to rapid death related to pulmonary oedema. It is considered a significant public health hazard (adapted from IPCS, 1982 and PHE, 2019).