The injuries caused by the blasts will tax the skills of the medical staff caring for the victims to the limit. Over the next couple of days the survival of the most badly hurt will hang in the balance.

Those with extensive burns and inhalation injuries caused by hot gases in the explosions will be in the most critical condition. Inhalation injuries can be among the hardest to treat because damage to the lungs affects capacity to absorb oxygen.

Those patients will be put on a ventilator in intensive care but there is no treatment other than "supportive" care. The way the lungs react varies from individual to individual. The young and fit tend to do better but even they can succumb. Some develop lung problems depending on their age and past history. There is always hope but, inevitably, not all those in intensive care are going to emerge alive.

Victims with extensive burns to their skin will require pain relief and care to replace the loss of fluid that leaks away through the seared tissue. Severe cases may develop major circulatory problems as blood pressure falls requiring fluid resuscitation.

Superficial burns will heal with repeated dressings but skin grafts will be required for more extensive injuries. Typically, victims needing immediate skin grafts will be in hospital for seven to 10 days but may have to return for further surgery later. The worst affected may face weeks or months in hospital.

Skin grafts over joints can cause contractures, hindering movement and further surgery is needed to improve the function and appearance of the graft.

Many of the victims suffered penetrating injuries caused by glass, metal and pieces of debris thrown out by the bombs.

Surgeons will have had to remove foreign bodies and repair any damage to internal organs or blood vessels.

Some victims will have escaped serious damage but others may have been severely injured depending on the size of the fragment, the force with which it hit and the area of the body struck. A large fragment hitting the thigh generally causes less damage than a small one striking the torso.

Ordinary fractures can be repaired by inserting metal fixings or setting the limb in plaster - but they are rarely ordinary in bomb blasts. Often there is extensive damage to the surrounding tissue which often means it requires skin grafting and reconstructive surgery.

People with chest injuries may have fractured ribs which, though painful, are not of themselves a problem. But they may conceal underlying damage to the lungs, heart or great blood vessels caused by the force of the blast.

Air or blood may become trapped in the chest and require draining by the insertion of a tube through the chest wall and ventilation. About one in 10 patients needs a thoracotamy - opening the chest to secure the blood vessels and prevent lung collapse.

Injuries to the head can be among the worst if they cause the brain to swell, increasing pressure and leading to long-term brain damage. Nothing can be done to repair the initial injury but, with the right care, it can be prevented from getting worse. Some patients can make a complete recovery while others do less well.

A scan will reveal the extent of the injury and whether surgery is necessary to remove a blood clot. Surgeons may place a device inside the skull to monitor the pressure.

The key to stop swelling is to keep the patient well ventilated, with good oxygen levels and circulation. Often the extent of the injury does not become clear for several days.

Victims of the bombs, whether they suffered physical injury or not, are likely to suffer psychological after-effects of the trauma including nightmares, flashbacks, anxiety and depression.

Some may suffer profoundly while, in others, the impact may be delayed. People who feel they should be able to cope, perhaps because they were uninjured, may find they can't. The effects may last years and some symptoms may not surface for a while.