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( By WHO - OMS, 1999 )

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9-Conducting the assessment

The rapid assessment consists of:

- confirming the existence of a chemical emergency;
- determining the source, site, type, size and distribution of the release;
- identifying the specific types of chemicals and their reaction by-products;
- determining the population at risk and the health impact; and
- assessing existing health response capacity.

Confirming the existence of a chemical emergency

The first alert or rumour that a chemical emergency is occurring may originate from a wide range of sources. A quick visit to the site by a person with knowledge of handling dangerous goods or chemical expertise, taking suitable precautions, is important to verify this information.

The health personnel conducting the assessment should investigate the following questions:

Has some incident happened involving chemical substances?
Has some incident happened in or around a chemical installation?
Has the community noted or have health facilities registered an increase in:

- irritation of the eyes, the skin, the mucous membranes?
- coughs, asthma, respiratory distress?
- neurological illness?

Clinical examination of a sample of cases will help confirm the emergency.

Determining the source, site, type, size, and distribution of the release

This information is essential for defining the populations at risk, the potential range of exposures resulting from the accident, and the measures to be taken.

The exact site and type of incident should be determined, especially since a chemical emergency may involve one or more types of release. Other key characteristics include the size of the release (estimated weight or volume of the chemicals dispersed) and its distribution pattern (which is affected by weather conditions).

Identifying the types of chemicals and their reaction by-products

It is necessary to identify the chemicals involved in order to:

- anticipate their likely harmful effects;

- develop working case definitions of exposed and injured individuals and set criteria for triage;

- determine medical treatment for the injured and need for specific medication, decontamination, and follow-up regimens for those exposed;

- provide protective equipment for rescue personnel; and

- initiate control measures for environmental clean-up.

The identity, quantity, and ambient air concentrations of the chemical(s) can be determined through:

- product labels (product name, UN Hazard Classification and UN Substance Identification number);

- contacting companies in charge of the manufacture, storage, transport, use or disposal of the chemicals;

- contacting chemical information centres; and

- environmental sampling.

The collection of samples from the environment (air, water, food, soil, foliage) is important, since many unknown by-products may be produced in fires and explosions.

Determining the population at risk and the health impact

Determine the population at risk. Gather information on the proximity and size of residential neighbourhoods, the location and numbers of high-risk populations (e.g. individuals with chronic illnesses, pregnant women, and infants).

Evaluate toxicological risks and human exposure pathways. Environmental exposure and body burden assessments are usually not feasible during the acute phase of the accident. These require complex sampling and labour-intensive analytical procedures.

Describe morbidity and mortality. For this to be done systematically, it is essential that a working case definition is developed, and consistently applied. During the actual emergency, it is not feasible to conduct a survey. However, it is important to collect information on whether there has been increased morbidity or mortality caused by the release.

Analysing the information

Time: When did the cases occur? Is their number increasing?

Plot the daily number of cases on a graph.

If the chemical accident has affected a wide area, plot a separate graph for each affected community.

Survey known exposed groups.

Place: Where have cases occurred? Are new cases being reported from other areas? Are there accessible, equipped, and safe health facilities in the affected areas?

Map the cases geographically.
Use maps that have health facilities identified.

Person: Which groups are at greatest risk?

Examine data on age, sex, occupation, and residence to identify highest risk groups.

Estimate the numbers of hospital admissions and outpatient attendances for affected areas and specific facilities.

Drawing initial conclusions

Has a chemical release occurred?
Has the causative chemical(s) been identified?
What are the main risks for human health?
How many cases or deaths so far?
What is the geographical distribution of the cases?
What is the size of the population at risk?
Do the effects of the accident appear to be spreading?

Assessing local response capacity

The response capacity of health services should be assessed with particular attention to determine the following:

- availability of first-line and backup emergency medical services (including health personnel and facilities);

- availability of protective equipment;

- use of clear diagnostic criteria, standard treatment regimens, and compliance with them;

- availability of specific medication (e.g. antidotes);

- availability of facilities for decontaminating exposed individuals (including health workers); and

- vulnerability of the health facilities to the chemical.