Chapter 28: Class B Fires Flashcards
Class B Fire:TDG/NFPA & WHIMS defined Flammable Liquid as
TDG: A Flammable Liquid as one that has a flash point 60.5’C
NFPA/WHIMS: Define it as one with a flash point below 37.8’C
Class B Fire & Explosion Prevention
5
- Exclusion of Ignition source
- Exclusion of air(O2)
- Storage of liquids in closed containers/systems
- Ventilation to prevent accumulation of vapor with in the flammable range
- Use of inert gas atmospheres
Extinguishment of class B
Shutting off fuel supply
Exclusion of air(vapor suppression)
Cooling to stop evaporation
Combination of these
Pressurized flammable gases have following characteristics
Pressure Diffusivity low boiling points colorless/odorless Creates static electricity when flowing
Safety release devices
Pressure relief valve
Rupture discs
Fusible Plugs
Gas color coding
Silver/Green: O2 Blue: Nitrous oxide Orange: Cyclopropane Brown: Helium Red: Ethylene Grey Carbon Dioxide
3 types of Container stresses
Thermal, Chemical, Mechanical
5 methods of Container Breach: stressed beyond their limits of recovery
Disintegration Runaway Cracking Attachments open Puncture Split
13 gases lighter than air
4H MEDIC ANNA
Hydrogen
Helium
Hydrogen Cyanide
Hydrogen Fluoride
Methane
Diborane
Illuminating gas
Carbon MonOxide
Acetylene
Neon
Nitrogen
Anhydrous Ammonia
container release types
Hemispheric Plume Cloud Cone Stream Pool
LPG(liquid petroleum Gas)
boiling point -90'C to -1.1'C Stored in pressurized vessels -Cylinders(454kgmax) -Tanks -Lines
Pressure Range 170-17000kpa
Term LPG =Propane, Propylene, n-Butane, Isobutane, and Butylene
BLEVE
Boiling Liquid Expanding Vapor Explosion
Bleve warning
Pressure relief device working pitch or sound gets loader Pings,pops,snaps Steam=above 100'C discoloration of shell & impingement bulged or bubble
if we have flame impinging on tank
Cool tank from top down Large tanks fail in 10-20 min use master stream appliance non survivable area of 500' water must not turn into steam it must reach container
Natural Gas
Explosive range 5-15%
Propane
1.5 x as heavy as air so it sinks
low ignition temp. 450”C
Foam Ops
- Foam creates a barrier between fuel and fire
- Lowers temp of fuel and adjacent surfaces
- Prevents release of flammable vapors
- Penetrates product to get at hot embers
3 steps of generating and applying foam
Proportioning
Foam Generation
Distribution
Proportining
Mixing foam concentrate with water
Most concentrates are to be mixed 94%-99.9% water
(6%max concentrate)
4parts foam con. + 96 parts water= 100 foam parts solution
We use Niagra A-B foam but there are 4 other types
AFFF: Aqueos film forming Foam: thin layer that covers liquid
Alcohol resistant: barrier against solvents
Fluoroprotein: below ground fuel tank
High-expansion foam: voids
Niagra A-B foam
Detergent free Can be properly discharged through all fog nozzles Long shelf life can be used with other foams can be used on both A & B fires
Class A foam %’s
- 1%: deep seated fire
- 1-0.5%: wildland/grass fire
- 5%: Structural FF w/fog Nozzle, wild land surface w/foam nozzle
- 0%: exposure protection Barriers for wild land
Class B Foam %
- 0% shallow hydrocarbon spills
- 0% on sever hydrocarbon spills and polar solvents
- 0% for Hazmat Vapor suppression
4 methods foam is proportioned
Induction:in-line eductor (old pump)
Injection: External pump forces foam into the fire stream
Batch mixing: pour foam directly into pumps water tank
Pre mixing:used in fire extinguishers
