The brigade has warned of the affects of tampering with fire hoses

Firefighters were dealing with a blaze in a skip in Poleglass, near Lisburn, when they were surrounded by a group of about 15 youths.

One of the youths interfered with the water controls, dramatically boosting the supply.

A firefighter was flung into the air and broke a bone in his back. A second sustained a twisted knee.

The firefighters had been holding the hose during the call-out in Collinbrook Crescent on Friday, when the youth flicked a switch on a water pump at the back of the fire appliance.

The men were tossed about as the hose flailed out of control.

That sudden increase in pressure lifted the firefighter off his feet and threw him to the ground Jim McAllen Fire Brigade

The more seriously injured crew member was treated in the Lagan Valley Hospital. He was later discharged.

The Fire Brigade said it was a "prank that went badly wrong", but that the power from a hose could not be underestimated.

The service said it was fortunate that no-one was killed.

Assistant Divisional Officer Jim McAllen said: "It would appear that rather than it being a malicious attack on the crews, one of the youths pulled the throttle control at the rear of the vehicle which operates the pump.

The firefighters were attending a blaze in a skip

"That dramatically increased the force of the water pressure in the hose.

"That sudden increase in pressure lifted the firefighter off his feet and threw him to the ground, where he struck his back and his side on the edge of the kerbstone."

Sinn Fein assemblyman Michael Ferguson condemned the incident.

"The person who did this was a fool," he said.

"He thought it would be funny to tamper with a fire hose so what he did was he went behind the engine and revved up the pump.

"It could have been deadly. Had the young fireman not held onto the hose, the nozzle could have lashed out and possibly killed one of the young people in the crowd."

SDLP councillor Margaret Walsh said the youths were "irresponsible".

"This type of loutish behaviour is totally unacceptable and those involved must take full responsibility," she said.

"Our emergency workers deal with extremely difficult situations and are there to serve the whole community. No-one has the right to put them under further stress or to attack them in any way."

The Fire Brigade has urged parents to make sure they know where their children are at night.