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Chemical incidents


    A chemical incident is the uncontrolled release of a toxic substance, potentially resulting in harm to public health and the environment. Chemical incidents can occur as a result of natural events, or as a result of accidental or intentional events. These incidents can be sudden and acute or have a slow onset when there is a ‘silent’ release of a chemical. They can also range from small releases to full-scale major emergencies.

    The term “chemical incident” might refer to anthropogenic or technological events, including:

    • an explosion at a factory that stores or uses chemicals
    • contamination of the food or water supply with a chemical
    • an oil spill
    • a leak from a storage unit during transportation
    • deliberate release of chemicals in conflict or terrorism
    • an outbreak of disease that is associated with a chemical exposure.

    Chemical incidents arising from natural sources include volcanos, earthquakes and forest fires. An estimated 65 000 people died due to technological events between 2009-2018.

    As the production and use of chemicals continues to increase worldwide the health sector must expand its traditional roles and responsibilities to be able to address the public health and medical issues associated with the use of chemicals and their health effects.


    Chemical incidents, especially acts of terrorism, may also cause fear and anxiety in populations, as well as injury from fire, explosion or toxicity. Depending on the chemical exposure, symptoms may present themselves differently.

    In general, the adverse health outcomes to toxic chemical exposure may be:

    • effects that are local or arise at the site of contact with the chemical, such as bronchoconstriction from respiratory irritants, or irritation of the skin and eyes by gases, liquids and solids;
    • effects that are systemic or affect organ systems remote from the site of absorption, such as depression of the central nervous system from inhalation of solvents, or necrosis of the liver from the inhalation of carbon tetrachloride; and
    • effects on mental health arising from real or perceived releases, which depend on the psychosocial stress associated with an incident.

    The time elapsing between exposure and the onset of symptoms can vary:

    • Some effects, for example eye and respiratory irritation or central nervous system depression, can occur rapidly, within minutes or hours of exposure.
    • Other effects, for example congenital malformations or cancers, may take months or years to appear.
    WHO Response

    WHO works closely with countries and partners to monitor and report on their emergency preparedness capacities for all hazards, including for chemical incidents. Surveillance of diseases of possible chemical etiology is a daily element in WHO’s outbreak alert and response activities. 

    WHO also convenes regional meetings to strengthen the global network of poison centres and thus facilitate emergency responses to chemical incidents. Guidance and training materials to strengthen preparedness for chemical incidents and emergencies have been developed in collaboration with the Organisation for Economic Co-operation and Development, the Inter-Organization Programme for the Sound Management of Chemicals, and relevant organizations in the United Nations system.

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