Flash-over

The time needed to evacuate an aircraft will clearly set a lower limit on the flash-over time and therefore limit the material choice. Flash-over is a highly dangerous condition and can be avoided with the above fire source by choosing a thermoplastic resin/fibre system (e.g. polyimide/ PEEK), or delayed by using an appropriate phenolic system (e.g. glass/ phenolic). 

Madgwick, T. (1988) Aircraft fire safety — are we meeting the challenge in Fire Performance of Materials in Mass Transport, RAPRA, Shawbury. 

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The major differences between ac and dc starters are necessitated by the commutation limitation of dc motors, which is the ability of the individual commutator segments to interrupt their share of armature current as each segment moves away from the brushes. Normally 250 to 275 percent of rated current can be commutated safely. Since motor-starting current is limited only by armature resistance, line starting can be used only for veiy small [approximately 1492-W (2-hp)] dc motors. Otheiwise, the commutator would flash over and destroy the motor. External resistance to limit the current must be used in starting to prevent this. 

Specimens are thin sheets or plates having parallel plane surfaces and are of a size sufficient to prevent flashing over. Dielectric strength varies with thickness and, therefore, specimen thickness must be reported. The dielectric strength varies inversely with the thickness of the specimen. The dielectric strength of plastics will drop sharply if holes, bubbles, or contaminants are present in the specimen being tested. 

Results full scale fire tests. The analytical results from six of the thirteen materials investigated in the full scale fire test art presented in Table II. The integrated amount of each gas from the start of the experiment until flash over in the room has occured i ... 

I So, like you said earlier, you wouldn t go in blue lights flashing over something like this ... 

Flashover The stage of a fire in which a room or other confined area becomes heated to the point that flames flash over the entire surface of the area. 

Impact damage occurred to one of 48 10 kg polypropylene tubs of calcium hypochlorite, each closed with a polythene lid, all supported on a wooden pallet and stretch-wrapped round the base with polyethylene film. The spilled material was swept up and discarded, and the pallet was moved to another part of the warehouse, and some 30 mins, later flames were seen at the base of the pallet [1], Ignition was attributed to contact between residual solid hypochlorite on the pallet and lubricant drips on the concrete floor from fork lift traffic. Application of a dry powder extinguisher had little effect on the fire, but use of a 40 1 water extinguisher led to rapid escalation of the fire as contact between hypochlorite and wood was increased. Flash-over occurred and the fire eventually involved a considerable fraction of the 1400 t of assorted warehouse contents [2],... 

When testing electric strength there is the risk of flash-over across the specimen surface between the electrodes. This is avoided by making the measurement with the specimen immersed in an insulating liquid, such as transformer oil, which displaces air from the ceramic surface. 

Estimate the steady state surface temperature above that of the air ambient assuming a rate of loss of heat of 10 W m 2 K 1, and comment on how this might affect performance in a polluted atmosphere. [Answers 1.5mm 60/rm 2.5K reduces risk of condensation on the glaze surface and so risk of flash-over ]... 

Several standard room/corner test protocols are now available and are specified in codes and regulations for qualifying interior finishes. For example, U.S. model building codes require that textile wall coverings for use in unsprinklered compartments meet specific performance requirements when tested according to NFPA 265. The principal requirement of these tests is that flash-over does not occur. The same codes also require that all other interior wall and ceiling finish materials comply with requirements based on NFPA 286, including a limit on the total smoke released. 

Detonation, Sympathetic Detonation. Flash over means the transmission of detonation from a cartridge to another one in line. Explosives with extremely high flash over tendency can be initiated by the shock wave from one charged borehole to the next one, even at large distances (- Ditching Dynamite). 

Detonation, Sympathetic Detonation. Flash over means the transmission of detonation from a cartridge to another one in line. Ex-... 

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