Humanitarian Health Action

Technical Hazard Sheet - Technological Disaster Profiles

Chemical and radiological incidents

The Hazard

Chemical incidents can be defined as accidental or intentional events that threaten to expose or do expose responders and/or members of the public to a chemical hazard.

Incidents can be sudden and acute, when hazardous chemicals are ‘overtly’ released into the environment. Incidents can also have an apparently slow onset, when there is a ‘silent’ release. The main scenarios are:

  • a detected release from a known chemical from a fixed site;
  • a detected release of a known chemical from a non-fixed site;
  • a detected release of an unknown chemical – typically, this will involve releases from sites not on a hazardous site inventory, illegal/uncontrolled dumping of chemicals, or unknown combustion products from a chemical fire; and
  • a silent release, where the release was usually unrecognised.

Chemical incidents may manifest their presence in one of two ways:

  • a failure in the containment of chemicals, with or without exposure of the public; and
  • an outbreak of illness.

The factors leading up to an incident include poor maintenance of manufacturing and storage equipment, lack of regulation and/or poor enforcement of safety regulations, road traffic accidents, human error, natural events such as heavy rain, earthquakes, hurricanes, floods, and terrorism.

Chemical incidents range from small releases to full-scale major emergencies.

Factors of Vulnerability

Most incidents occur at the interfaces between transport, storage, processing, use, and disposal of hazardous chemicals, where these systems are more vulnerable to failure, error or manipulation.

Common measure to reduce vulnerability and health risks of chemical incidents are:

Exposure levels will in general be quite different for different people involved in a chemical incident:

  • employees and other on-site persons -- usually more than one exposure pathway, often inhalation of vapour and skin contact from splashing and clean-up;
  • emergency services – usually close to the emergency and involved in rescue, containment of chemicals, putting out fires; primary and secondary contamination of fire officers, ambulance officers, other emergency staff; secondary contamination of medical staff and other hospital patients of incomplete decontamination of causalities;
  • public – exposure via air, water, food, soil etc.

Factors that affect the vulnerability of responders and the public include the nature of the hazard, the level of exposure, availability and quality of shelter, availability of Personal Protection Equipment (PPE), access into and out of the site, the degree to which employees and responders (and possibly the public) are prepared and trained to deal with an chemical release and the amount of training provided. Vulnerability can be reduced by ensuring that information is available on:

  • the incident;
  • measures being taken to contain the release;
  • who is currently under threat;
  • what the health effects might be from exposure;
  • what the public can actually do to protect themselves; and
  • how to get further information; when, where and how it will be available.

Some individuals and sub-populations can also be at increased risk because they are more susceptible to the adverse effects of a given exposure. Among the potential causes of enhanced susceptibility are inherent genetic variability, age, gender, pre-existing disease (e.g. diabetes, asthma), inadequate diet, occupational, environmental or lifestyle factors (e.g. smoking), stress and inadequate access to health care.

  • locating chemical sites away from centres of population;
  • registration of all chemicals in commercial establishments with a hazard inventory to ensure rapid identification of the released chemical;
  • regular evaluation of plans and their implementation;
  • inspection/monitoring and enforcement of safety measures;
  • reducing the amounts of chemicals stored;
  • appropriate labelling of all chemicals;
  • rapid notification of the chemical incident emergency services in the event of a chemical release;
  • regular surveillance and standardized reporting of incidents, including the small “routine” ones;
  • measures to decontaminate land or water already contaminated by waste disposal;
  • measures to prevent or contain fire-fighting water run-off;
  • construction of drainage ditches or holding tanks to contain liquid chemicals.

Main causes of Mortality and Morbidity

In most cases the mechanisms and health outcomes of exposure are unknown. Symptoms may present themselves differently depending upon the chemical involved. 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 (acute effects).
  • Other effects, for example congenital malformations or cancers, may take months or years to appear (delayed effects).

The duration of the symptoms can also vary, from short term, to long term or chronic.

Chemical incidents (especially acts of terrorism) may also cause fear and anxiety in populations.

Foreseeable Needs

In any chemical incident, there are a number of essential steps to go through as part of the chemical incident plan. These are in an approximate chronological order:

  • alerting the health care services;
  • best outcome assessment of actions and management options;
  • public information and public warnings;
  • advice on protection;
  • sheltering or evacuation;
  • other restrictions to protect public health;
  • organizing registers and samples;
  • collections of (human) samples;
  • environmental monitoring.

Don’t Forget


That careful planning and thorough preparedness are prerequisites for an effective response to chemical incidents.

That public authorities, at all levels, and the management staff of installations where hazardous chemicals are produced, stored etc. should establish emergency preparedness plans.

That all responsible parties should ensure that manpower equipment, and financial and other resources necessary to carry out emergency plans are readily available for immediate activation in the event, or imminent threat of an accident.

That all personnel involved in the emergency response process should be adequately educated and trained.


That depending on the level of potential exposure, risk zones are usually established around an incident:

  • The hot zone, is the area where first responders must use protective equipment to prevent primary contamination;
  • The warm zone, which surrounds the hot zone, is the area where appropriate personal protective equipment must be worn to prevent secondary contamination;
  • The decontamination line separates the warm from the cold zone; and

That a vulnerable zone (in effect a potential hot zone) can be declared, which is the area likely to be contaminated if the emergency response action are not successful. The population within the vulnerable zone includes the resident population as well as the working population (in the plant and in the area), and other populations in the area at certain times, such as motorist, tourists and visitors to entertainment facilities.

To set-up a public health team which, in case of an chemical incident, will provide accident and emergency departments with information about the nature of the chemicals(s), any precautions to be taken, and information about secondary contamination and how to decontaminate causalities, staff and equipment.

To contact the nearest Poisons Centre in case advice on diagnoses and treatment of chemical poisonings is needed. A list of global Poison Centres is available from the WHO INTOX Progarm WHO INTOX can also be contacted at The directory provides a means for obtaining

  • information needed in preparing, or responding to , chemical incidents;
  • advice in establishing emergency response centres or programmes; and
  • technical assistance in dealing with a response to a particular incident.

The importance of communication in a crisis situation to avoid unnecessary panic and fear.

Inappropriate Response

Ignorance and poor preparedness e.g. in not understanding the importance of adequate decontamination so that ‘dirty’ victims are allowed into clean zones, thereby increasing the number of people exposed to the chemical.

Panicking, and evacuating the public when it would be better to advise them to stay indoors and close all windows etc.

Ignorance and poor investigation of potential delayed and long-term effects and to assume that once the acute incident phase is over and the acute health effects are dealt with there are no additional potential health problems in exposed populations.

Prepared by:

International Programme on Chemical Safety (IPCS) for the Department of Emergency and Health Action in Crises, World Health Organization, Geneva, Switzerland Please contact: for further information.

Contacts for specific related topics, please contact: Chemical incidents, Dr K. Gutschmidt tel +41 22 791 3731 or

For information on chemicals,diagnosis and treatment:

The International Programme on Chemical Safety IPCS INCHEM database is available on the web free of charge at IPCS INCHEM is a means of rapid access to internationally peer reviewed information on chemicals commonly used throughout the world, which may also occur as contaminants in the environment and food. It consolidates information from a number of intergovernmental organizations whose goal it is to assist in the sound management of chemicals. IPCS INCHEM includes the following collections of publications:

  • IPCS Environmental Health Criteria monographs
  • IPCS Concise International Chemical Assessment Documents
  • IPCS Health and Safety Guides
  • IPCS International Chemical Safety Cards
  • WHO/FAO Pesticide Data Sheets
  • JECFA monographs
  • JMPR evaluations
  • IPCS Poisons Information Monographs
  • IPCS/EC Evaluation of Antidotes Series
  • ILO/CIS Chemical Database
  • UNEP-processes OECD Screening Information Data Sets

The IPCS INTOX database is available on the web free of charge at This database is an essential source of toxicological information. It includes the following internationally peer-reviewed documents:

  • Poisons Information Monographs
  • Treatment Guides
  • Antidote Monographs
  • Environmental Health Criteria Monographs
  • International Chemical Safety Cards
  • WHO/FAO Pesticide Data Sheets
  • a worldwide list of poison centres
  • others.

For further reading

Tools for assessing chemical risk