The lack of preparation for traumatic conditions and counselling not only harms the workers, but also the populations they seek to serve, say researchers.

But aid workers say there have been improvements in recent years, although there is still some way to go.

Writing in the British Medical Journal, Dr Maureen McCall and Dr Peter Salama say procedures for ensuring staff are psychologically equipped to work in emergency situations vary greatly among aid agencies.

A survey and interviews with 12 of the leading humanitarian relief organisations based in Europe and the USA, found that some recruited staff based on a single telephone interview while others had a full day of individual and group interviews.

In acute emergencies, staff were less likely to go through formal procedures.

Natural disasters

There was also a big variety in the way staff were prepared for dealing with a complex humanitarian crisis.

The researchers say these are more traumatic to deal with than natural disasters since they can involve threats to the lives of the workers as well as many moral dilemmas, such as negotiating with warlords and witnessing human rights abuses but being unable to respond to them because of operational restraints.

One organisation said it had actually employed workaholics and alcoholics on purpose because "some situations require people who can destroy themselves and thrive on chaos".

Organisations said it was difficult to ascertain whether a person was psychologically fit to deal with a humanitarian crisis.

Some staff health officers said they were not called in until after staff had been recruited, meaning they had virtually no say in their psychological screening.

Stigma

Most organisations said there was not enough support for staff once they were working in a crisis situation.

Medical workers in particular were worried about the stigma associated with mental health problems and steered clear of counsellors, preferring to resort to alcohol and drugs.

"One of the consequences of the apparent ad hoc nature of current practices may be an unnecessarily high prevalence of psychological morbidity (ranging from "burn out" to classic post-traumatic stress disorder) that is as yet inadequately documented and awaits further research," write Drs McCall and Salama.

They recommend that standards be set for selecting relief workers, that methods for detecting psychological vunlerability be developed and that more emphasis be placed on psychological trauma when preparing missions abroad.

They also call for organisations to keep better long-term records on the psychological health of staff who have worked in crisis areas.

Somalia

However, Gay Harper, staff health officer for the Save the Children Fund, said that things had been improving since the Somalia crisis, which she described as "a turning point".

People in Aid, a group set up after a recent report on aid agencies' recruitment policies, is trying to get organisations to sign up to a voluntary code of conduct to improve their procedures.

Ms Harper said most agencies now took the psychological health of their staff very seriously and offered counselling and debriefing sessions.

Many aid workers are ill-prepared for the psychological impact of crisis work

She has worked as an aid worker and feels this helps staff to confide in her because she can understand many of the problems they face.

Save the Children Fund (SCF) stresses that staff should take regular breaks from crisis work and encourages workers to take care of each other.

This may involve reporting to headquarters if they have concerns about the psychological health of a colleague.

"One of the major problems is burn-out after many years of working on crises.That is why we have a rest and recuperation policy.

"It is important for people to have breaks and that they do not stay in one place for a long time as this kind of work can wear away at the soul," she said.

SCF tries to ensure staff it hires are psychologically suitable for aid work at interview and through an intensive induction course.

It is now looking at ways of providing support to nationals working on the ground with foreign staff.

But services have to be developed which are appropriate for different cultures.