TB 7 - Fighting Fires with Large Spray Streams Flashcards
Advantages of Spray Streams:
- Greater SURFACE AREA of cooling
- More efficient use and less water damage due to more COMPLETE TRANSFER of HEAT
- Smaller water droplets RAPIDLY convert into vapor (REDUCING surrounding 02)
- SHIELDING personnel from RADIANT heat and can make an area MORE TENABLE where heat and smoke constitute a serious hindrance to firefighting.
- Greater COVERAGE area due to wider angle of stream
- More easily managed at higher PSI and delivering more GPM.
- More effective on some flammable liquid and electrical fires
Disadvantages of Spray Streams
- Less reach due to “SKIN FRICTION” (water vs air)
- “Skin friction” causes entrained AIR to be DIRECTED toward fire. (May or may not be desirable)
- Some spray droplets MAY NOT be large enough to REACH heated area around fire due to WIND or drafts
- Large fires demand good REACH and VOLUMES of water. Spray nozzles CANNOT DO BOTH simultaneously.
- Creates more HOT STEAM which may make a confined area temporarily UNTENABLE
Water expands into steam at a ratio of 1 to ______ with 1 gallon of water capable of producing about 227 cubic feet of vapor.
1700
1 gallon of water absorbs _____ BTU in changing to steam
9330
The PHYSICAL differences between spray streams and standard straight streams are:
-SIZE of water droplets
-SHAPE of stream
-Effective REACH
Spray streams are of excellent value in killing the heat of a large body of flame if accompanied by?
sufficient VOLUME of discharge.
(VOLUME of water is generally MORE IMPORTANT than any excess in pressure over that necessary to produce a stream which will reach the seat of the fire.)