Natural disasters

Earthquakes

Movements of the Earth's crust create tremors below ground every day; fortunately the vast majority are out at sea. The point nearest to the surface is the epicentre and marks the site where the quake is strongest. Force is measured on the Richter scale—a logarithmic scale, so that a force 7 quake is 10 times stronger than force 6 and 100 times stronger than force 5. When earthquakes occur near to or on land, the major danger is from building collapse. Survivability is not always related to building height. Falling debris and entrapment pose the greatest risks.

Search and rescue

Most successful rescues take place within the first 24 hours. Most lives are saved by the immediate actions of survivors. Local authorities implement the second phase, when a more coordinated response is established with local rescue teams joining the survivors. In the third phase more intensive and focused efforts are supplemented with extra help from other areas. The fourth and final phase involves the provision of specialist aid for rescuing people deeply entrapped.

Risks associated with entrapment after an earthquake

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Up to three times as many people are injured as are killed, presenting an enormous burden to local medical facilities. The combination of injury and entrapment places a limit on survival. Major head and chest injuries are usually fatal. Peripheral limb injuries are the commonest surgical problems, and the effects of crush injury are the most complex.

Aftermath of the 1988 Armenian earthquake. The unburied dead pose little or no risk to the living

The greatest effects of earthquakes will be non-medical, with the loss of communication, transport, and power. Water supplies can be disrupted but are rarely contaminated. Fear of the unburied dead as a reservoir for disease is unfounded.

Floods

Although the immediate impact on survivors is likely to be injury and the death of relatives, damage to crops, housing, and infrastructure can conspire to precipitate acute food shortages and homelessness. Water supplies may be contaminated with sewage, leading to disease.

Volcanic eruption, Cape Verde. The eruption itself caused few deaths and injuries, but a cholera outbreak followed the mass evacuation of local people to tented accommodation

Famine

Famine may complicate all “natural” and human made disasters, and socioeconomic and political issues lie at the roots of cause and prevention. Trigger levels for urgent humanitarian intervention include a rise in crude mortality to 1 in 10 000 a day, pronounced wasting (loss of > 15% of normal body weight), and food energy supplies of < 1500 kcal (6.3 MJ) a day.

Children are among the most vulnerable during famine

An adequate response requires planning and coordination at national and international levels. Famine, like other “natural disasters,” leads to the mass movement of people. It is a cause or consequence of other humanitarian crises including complex emergencies—where conflict compounds humanitarian needs and responses.

Hurricane Andrew and health coordination

Three days after Hurricane Andrew struck south Florida in August 1992, epidemiologists performed a rapid needs assessment using a modified cluster sampling method. Firstly, clusters were systematically selected from a heavily damaged area by using a grid laid over aerial photographs. Survey teams interviewed seven occupied households in each selected cluster. Surveys of the same area and of a less severely affected area were conducted seven and 10 days later, respectively.

Hurricane Andrew, one of the most destructive hurricanes in US history, inflicted widespread damage

Initial results, available within 24 hours of starting the survey, found few injured residents but many households without working telephones or electricity. Relief workers were then able to focus on providing primary care and preventive services rather than diverting resources towards unnecessary mass casualty services. This represented the first use of cluster surveys to obtain population based data after a natural disaster (previously they had been used in refugee camps to assess nutritional and health status).

Medical services were severely affected: acute care facilities and community health centres were closed, and doctors' offices destroyed. State and federal public health officials, the American Red Cross, and the military established temporary medical facilities. Within four weeks after the hurricane, officials established disease surveillance facilities at civilian and military centres providing free care and at emergency departments in and around the disaster area. Public health workers reviewed medical logbooks and patient records daily, and recorded the number of patient visits using simple diagnostic categories (such as diarrhoea, cough, rash).

This surveillance allowed the health status of the affected population to be characterised and the effectiveness of emergency public health measures to be evaluated. Surveillance information was particularly useful in refuting rumours about epidemics, so avoiding widespread use of typhoid vaccine, and in showing that large numbers of volunteer healthcare providers were not needed.

Although the surveillance achieved its objectives, there were several problems. Data from the civilian and military systems had to be analysed separately because different case definitions and data collection methods were used. There was no baseline information available to determine whether health events were occurring more frequently than expected. Also, rates of illness and injury could not be determined for civilians because the size of the population at risk was unknown.

Although proportional morbidity (number of visits for each cause divided by the total number of visits) can be easily obtained, it is often difficult to interpret. An increase in one category (such as respiratory illness) may result from a decline in another category (such as injuries) rather than from a true increase in the incidence of respiratory illness.

This is the second in a series of 12 articles

Anthony D Redmond is emeritus professor of emergency medicine, Keele University, North Staffordshire.

The ABC of conflict and disaster is edited by Anthony D Redmond; Peter F Mahoney, honorary senior lecturer, Academic Department of Military Emergency Medicine, Royal Centre for Defence Medicine, Birmingham; James M Ryan, Leonard Cheshire professor, University College London, London, and international professor of surgery, Uniformed Services University of the Health Sciences (USUHS), Bethesda, MD USA; and Cara Macnab, research fellow, Leonard Cheshire Centre of Conflict Recovery, University College London, London. The series will be published as a book in the autumn.

The case study of Hurricane Andrew and health coordination was supplied by Eric K Noji, senior policy advisor for emergency preparedness and response, Centers for Disease Control and Prevention, Washington Office, USA. The picture showing damage from Hurricane Andrew was taken by Bob Epstein and supplied by the Federal Emergency Management Agency (FEMA).