Armed groups sometimes kill aid workers rather than kidnapping them. Robbery and rape are also routine dangers in the lawless societies where they work. But there is no shortage of volunteers - some are even attracted by the danger - and agencies turn many unsuitable candidates away.
Rebel fighting in Liberia has prompted one of the largest aid agencies in the region, Save The Children (SCF), to withdraw its staff to the capital, Monrovia. Yet Merlin, the agency for which three of the kidnapped Britons worked, insisted before their release that they were all qualified and experienced enough to decide whether or not to stay in the field.
The days have long gone when eager young people with a mission to save the world could call up an aid agency to inform them they wanted to help poor people. "We get a surprising number of calls like that, but we just politely pack them off to gap year organisations," said one personnel officer with a frontline aid charity.
Today, all such agencies take recruitment very seriously. Most people who sign up for a non-governmental organisation must have previous experience abroad and have practical training - as doctors, logisticians, and engineers. The selection of volunteers is seen by many as crucial in establishing safety for the agencies in the field.
"Security is not about assault courses and barbed wire around a compound," said Peter Hawkins, head of SCF's emergency unit. "Security starts with recruiting the right person. That means people who can cope with the stress, contribute to analysis of a situation, have logistical skills and an understanding of the cultural and political context they work in."
Merlin says it is careful to weed out anyone with a vague wish "to help the developing world". It has around 60 staff in the field in countries including Sierra Leone, Albania, Tajikistan and the Democratic Republic of Congo. All its volunteers are qualified doctors, nurses or logisticians. "Our people are trained to fly out into disaster zones and do a job," said a spokeswoman for Merlin. "They have comprehensive security training before they go out. The people taken in Liberia are all professional humanitarian aid workers who have worked with us before."
The British Red Cross, which has some 120 Britons abroad, spread across 39 countries, runs a prestigious week-long basic training course, during which it screens prospective candidates and trains them in international humanitarian law. "We use the week to watch people very closely and see whether they are suitable," said Pauline Dodds, international personnel officer who worked as a medical delegate through the British Red Cross for eight years. "You get a feel for people. The majority have purely humanitarian motives. They are skilled professionals who believe in what they are doing and want to share their expertise."
Nevertheless, even some of these qualified staff return home with inflated egos. Many aid agencies remain uneasy with the small number of people who sign up because they are attracted by the risks involved. "Some of these people come back effectively saying `I've been shot at - that makes me a better person than you,' which makes you wonder what their motives really are," said one senior delegate.
Aid workers in Liberia are only too aware of the risks, but feel they are outweighed for the time being by the need to help. Nathalie Ernoult, of Action Contre La Faim (Action Against Hunger) - said: "We must never lose sight of our mission, which is to help civilians, whatever the prevailing, politically correct view is. That means we have to talk to rebels and anybody who can help guarantee safety for our convoys and staff. It sometimes means taking risks."
Guy Millington, 29, from Malvern, was a City metals trader before going into full-time aid work, both with Merlin and Medecins sans Frontieres (MSF). "This is what I had always wanted to do," he said, "but after studying political sciences I got caught up in the rat race, which I finally left in 1996 to go climbing and paragliding."
Mr Millington, who used to deliver food to soup kitchens in London in his spare time, has worked in refugee camps in Peru and in Afghanistan with Merlin. Now in Sierra Leone, he is a "loggie", or logistician, who helps assess needs and arrange the infrastructure medical staff require before they can begin work. This can be one of the riskiest areas of aid work, as it involves being first on the scene. He was in Makeni, northern Sierra Leone, last week, when a group of other MSF staff were briefly taken hostage by rebels. He had to pull out two days into a five-day mission.
In 1992, Jackie Ryan, from Durham, qualified as a teacher but then left almost immediately for Tanzania where she worked for Voluntary Service Overseas (VSO). Since then she has hardly returned to Britain and has been a logistician in Tanzania, Bosnia, Sudan, China, Uganda and now Sierra Leone. As country manager for MSF-Holland, she is responsible for around 75 staff, including 14 expats. "I do think about the dangers; the entire expat staff is my responsibility and the Occra Hills incident [the recent mass kidnapping involving British military officers] makes you look again at security."
Threats to aid workers have intensified in recent years. Ironically, recent kidnappings have come as the International Committee of the Red Cross (ICRC) marks the 50th anniversary of the Geneva Conventions, optimistically known as the laws of war, which set humanitarian limits to military action and offer greater safeguards for civilians. According to the United Nations, before 1992 it was almost unknown for a UN staff member to be killed; since then more than 150 have died.
The ICRC has perhaps the most dangerous role of all - a mandate to enter war zones and other conflict situations and negotiate the release of hostages - but it was stunned by the murder in cold blood of six of its workers in Chechnya in 1996, when rebels entered a compound, shattering the notion that the Red Cross and Crescent symbols were inviolable. "That made people very wary," said one aid delegate who has worked with volunteers from several charities. "The risk is much greater today because there are so many ad hoc guerrilla groups who have never heard of the Red Cross and simply don't recognise it."
"Aid work is more dangerous than it was 15 years ago," said Peter Hawkins of SCF, which works in 70 countries, including Rwanda, Sudan, Afghanistan, the Democratic Republic of Congo and Sierra Leone. "That has nothing to do with the aid business and more to do with the nature of conflict. They tend to target civilians ."
Oxfam, which has 170 British staff in 70 countries, including 45 in Africa, also places great emphasis on gaining recognition from all sides in a conflict. "There's a perception that the threat to aid workers is increasing," said Oxfam's Charles Walker. "The increase in civil wars might be a reason for an increased threat. Acceptance can break down where there is banditry or ill-discipline, and the Geneva Conventions need a certain amount of discipline to be enforced."
Oxfam, along with several other agencies, withdrew from Liberia in 1996, believing the dangers seriously impeded the ability of its staff to carry out their work. "The fighting groups found our vehicles and radios very attractive for their own purposes," said Mr Walker. "If the risks are so great that we cannot work effectively, there is no point in being there."