Rollover (fire)

A smoke (gas) by ignition (English roll-over ) is the sudden By igniting and burning of pyrolysis gas. This gas mixture is produced by the action of heat or combustion. In a flue gas ignition, primarily in dedicated rooms, enough oxygen for ignition is present. This distinguishes the smoke gas ignition of the flue gas explosion ( backdraft ), the flue gas further oxygen must be supplied for the first ignition. Main components of the flue gas is pyrolysis.

Operation in a locked room

Development phase

It develops a fire and heated, with sufficient oxygen present, the room and its constituents, so that pyrolysis gases form (wood and plastic gases from flammable materials ). These are thermally processed.

Full fire phase

Here it can when it reaches the ignition point for flue gas ignition and after full fire phase, including with flame blow out the windows to come.

Decrease phase

Then it often comes after the first full fire to a heat lift of the accumulating smoke. This fills the space up to the bottom and displaces the oxygen. The result is a decrease in fire intensity. Due to the incomplete combustion of the combustible carbon monoxide is generated with the smoke; for combustion the conditions necessary energy and fuel are now back in place. Is again supplied with oxygen, for instance by opening a door, it may be a flue gas explosion.

Origin

Pyrolysis gases are formed when a substance is heated to the extent that it secretes flammable gases. Examples of pyrolysis gases are the pungent yellow-white smoke of a campfire, like smoke from straw fires or smoke after blowing out a candle. This smoke (gas and particle mixture ) is flammable, which is easy to observe about candle if you hold a burning match a few centimeters above the smoldering wick away. Pyrolysis gases occur very easily on the fire of home furnishings, since in their production much plastic is used.

Pyrolysis gases are very hot and collect in the upper part of the room, heated by high temperature and other objects and cause them also to release pyrolysis gases. If the room is now open, flows into fresh air with oxygen, which is mixed with the combustible pyrolysis gases, and there is an ignitable mixture. Due to the already burning fire in space, the mixture is ignited and the environment heats up abruptly. By this enormous heat and pressure increase sudden burst even window. This fire may expand geographically on.

Why should enclosed spaces in which a fire is burning, can not be opened from unprotected and untrained people. But for members of the fire department is a smoke gas ignition is a not to be underestimated danger which might result in temperatures of over 1000 ° C.

" Roll-over " and " flash-over "

• When roll-over is the ignition of the pyrolysis of a smoke layer. Once there is enough combustible pyrolysis products have accumulated in the smoke layer and enough air to ignite the room is a through- ignition of the smoke layer takes place.
• During flashover is the transition from the initial fire to full fire by igniting all combustible surfaces in the room by the radiant heat of the smoke layer.

The phenomena flue gas ignition and flash-over occurs at every major fire in an enclosed space that exceeds the initial phase.