CHAPTER 1
The epidemiology and incidence of major incidents

Learning outcomes

After reading this chapter, you will be able to:

• Define and classify a major incident
• Identify the type of major incidents that can occur
• Describe the incidence of major incidents

1.1 Introduction

A major incident is said to have occurred when an incident requires an extraordinary response by the emergency services. While major incidents may affect any of the emergency services, the health service's focus is the resulting casualties. A major incident cannot, however, simply be defined in terms of the number of casualties - the resources available at the time of the incident are also relevant. For example, a road traffic accident in a remote area producing five multiply injured casualties may overwhelm the immediately available local resources. However, a similar incident in a major urban conurbation may require little or no additional resources. Thus, the same incident in different localities may produce a major incident in one but not in the other.

For the purposes of planning, major incidents have been defined as:

Events that owing to the number, severity, type or location of live casualties require special arrangements to be made by the health services.

Local highlights: Major incident definition

This definition is an operational one that recognises that major incidents occur when the resources available are unable to cope with the workload from the incident. The need to relate major incidents to the availability of resources is most clearly demonstrated when considering incidents that produce 'specialist' types of casualties. An incident producing paediatric, burned or chemically contaminated casualties may require the mobilisation of specialist services even when there are only a few casualties. This is because the expertise and resources needed to deal with these types of casualties are limited and widely scattered around any country.

Incidents such as plane crashes may occur in which all casualties are dead at the scene. Whilst these are clearly major incidents for the police and fire service, there is often little requirement for the health service beyond mortuary and pathology services. An example of such an incident is an air crash where all passengers are killed and only a few people are injured on the ground.

1.2 Classifying major incidents

Whilst the health service definition is an adequate one for planners at a local level, it does not tell us anything about the size of the incident or the incident's effect on society as a whole.

Rutherford and de Boer (1983) have classified and defined major incidents with regard to their size and effect on the health service and society. This classification system is useful for emergency planners and researchers. Their system defines major incidents in three ways:

1. Simple or compound
2. Size - minor, moderate or severe
3. Compensated or uncompensated

Simple or compound

Compound incidents are those in which the incident destroys the infrastructure of society itself. Roads, communications and even the health services may be destroyed, inaccessible or unavailable. Compound incidents typically arise as the result of war, terrorism or natural disasters. A simple incident is an incident in which the infrastructure remains intact.

Size - minor/moderate/severe

While it is not possible to decide whether a major incident has occurred purely on the number of casualties involved, an appreciation of the size of the incident can assist in the planning process for a major incident response. Rutherford and de Boer (1983) divide incidents into minor, moderate or severe (Table 1.1).

Table 1.1 Size classification of major incidents

Compensated or uncompensated

By definition, major incidents require the additional mobilisation of resources in order to deal with the health service workload. Incidents may be considered to be compensated if the additional resources mobilised can cope with the additional workload. When an incident is such that even following the mobilisation of additional resources the emergency services are still unable to manage, it is said to be uncompensated.

Failure to compensate may occur in three circumstances. First, the absolute number of casualties may be so large as to overwhelm the available health service resources. Second, the resulting casualties may require such specialised (or rare) skills or equipment that any more than a few casualties overwhelm resources. Such incidents may require relatively few casualties to reach this point, as there may be scant resources available to deal with them. Third, incidents occurring in remote areas may remain decompensated as the health services may be unable to reach the casualties.

The point at which decompensation occurs is often difficult to define and in many respects depends on the perspective of the observer. Total failure of the response to a major incident (such as the absence of any medical care) is clearly failure to compensate, and is most likely to occur in natural disasters or war. However, failure to compensate may also be considered to have occurred when the care given to individual patients is of a standard less than that acceptable in day-to-day practice. For instance, if there are many seriously injured casualties, specialist trauma networks may be overwhelmed and patients may be treated in facilities unused to treating severe injury. Decompensation is only considered to have occurred when the system fails to such an extent that individual patient care is seriously compromised.

At the present time little is known about the effectiveness of the health services' response to major incidents as this information is rarely recorded or analysed. However, anecdotal evidence suggests that the care given to individual patients during major incidents is often below the standard that would be delivered in normal daily practice.

1.3 The all hazards approach and special major incidents

Major incident planning should follow an 'all hazards approach'. This means that one basic major incident plan should be able to cope with all types of major incident. This is necessary as it is impossible for any emergency planner to predict the nature of the next incident. In addition, maintenance of separate major incident plans for all possible eventualities would be impractical. The all hazards approach also allows planning to be kept as simple and as near to normal working practice as possible.

However, despite these guiding principles, there are still certain types of incident that require additional modifications to the basic plan. This is the only way to achieve the aim of optimal clinical management for as many casualties as possible.

Incidents involving chemicals, radiation, burns, infectious diseases or large numbers of children are considered by many emergency planners as 'special' types of major incidents. Whilst it may be necessary to alter or embellish major incident plans to deal with these specific types of incidents, the required modifications should be made without significant departure from the basic (all hazards) major incident plan. All these incidents are characterised by a type of casualty for which resources may be scarce. They may, therefore, result in a failure to compensate by the health services' response even though there are relatively few casualties. Although these types of incident are considered separately, the general principles of emergency planning must still apply.

1.4 Natural disasters

It is worthwhile reiterating the difference between man-made and natural disasters when considering the epidemiology of major incidents. Natural disasters result from earthquake, flood, tsunami, volcano, drought, famine and/or pestilence. The potential for suffering and loss of life is enormous (Table 1.2).

Table 1.2 Natural disasters

On a world scale, natural disasters are important but require a different type of response to the simple, compensated major incident more...