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Low Expansion Foam
• NFPA 11
• class B– flammable liquids, FP < 1000F– combustible liquids FP > 1000F
• forms blanket
• 2-D horizontal surface
• tank farms, airports etc.
Expansion Ratio
Classification Range
Low expansion up to 20:1
Medium 20:1 to 100:1
High 200:1 to 1000:1
Components of Foam
Air– within bubbles– most of volume
Concentrate– to be mixed with water– final concentration 3% or 6%
Water– water + concentrate = solution
Types of Foam
Protein– older type– no film– from animal protein– little in use now
Types of Foam
Fluoroprotein– better than protein– forms film
Types of Foam
Aqueous Film Forming Foam– AFFF– most common for fuels– thin film– not for alcohols
Types of Foam
Alcohol Resistant– also “Alcohol type”– for small alcohols– methanol, ethanol etc– from membrane bewteen water and foam
Types of Foam
Chemical– chemically generated foam– obsolete
Proportioning Methods
• To mix concentrate with water
• either 3% or 6% concentrate in water
• 3 mechanisms– Venturi proportioner– Pressure proportioner– Balanced pressure proportioner– skip details
Types of Systems
Mobile– fire dept. trucks
Semi-Fixed– permanent piping, foam makers– mobile concentrate and pump
Types of Systems
Fixed– Subsurface injection– Surface application– seal protection for floating roofs– dike protection
Sub-Surface Injection
• Fixed roof storage tank
• foam applied below surface
• floats to surface
• gentle, uniform application
• fluoroprotein foam
• has good fuel-shedding properties
Sub-Surface Injection-design
1. Calculate fuel surface area
A =( )( r)2
2. Determine application rate (R) and discharge time (T)
• see 3.8
Sub-Surface Injection-design
3. Calculate discharge rate (D) and foam concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of subsurface application outlets
• see 3.9
Sub-Surface Injection-design
5. Determine supplementary requirements– number of hoses (see 3-10)– discharge time (see 3-11)
6. Calculate supplementary discharge rate (Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Sub-Surface Injection-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.1
Surface Application
• Fixed discharge units
• on rim of tank
Surface Injection-design
1. Calculate fuel surface area
A =( )( r)2
2. Determine application rate (R) and discharge time (T)
• see 3.14
• note difference between types I and II
Surface Injection-design
3. Calculate discharge rate (D) and foam concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of surface application outlets
• see 3.15
Surface Injection-design
5. Determine supplementary requirements– number of hoses (see 3-10)– discharge time (see 3-11)
6. Calculate supplementary discharge rate (Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Surface Injection-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.2
Seal ProtectionFloating Roof Tanks
• No vapour space
• gap at edge of roof a problem
• seal spans gap
Floating Roof Tanks-design
1. Calculate fuel surface area
A = total roof area - unprotected roof area
A =( )( r1)2 - ( )( r2)2
2. Determine application rate (R) and discharge time (T)
• R = .30 gpm/ft2
• T = 20 min.
Floating Roof Tanks-design
3. Calculate discharge rate (D) and foam concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the spacing of outlets
• see text
Floating Roof Tanks-design
5. Determine number of discharge devices
N = C/S
N = number
C = circumference ( x diameter)
S = maximum spacing
Floating Roof Tanks-design
6. Determine supplementary requirements– number of hoses (see 3-10)– discharge time (see 3-11)
7. Calculate supplementary discharge rate (Ds) and foam quantity (Qs)
Ds = (N) x (50 gpm)
Qs = (N) x (50 gpm) x (Ts) x (%)
Floating Roof Tanks-design
Total requirement for concentrate
Qtotal = Q + Qs
see example 3.3
Dike Protection
• To contain tank farm
Dike Protection- Design
1. Calculate dike surface area
A = dike length x dike width
2. Determine application rate (R) and discharge time (T)
R = .10 gpm/ft2 fixed outlets
R = .16 gpm/ft2 monitors
T = 30 min., flamm. liquids
T = 20 min., comb. liquids
Dike Protection- Design
3. Calculate discharge rate (D) and foam concentrate quantity (Q)
D = (A) x (R)
Q = (A) x (R) x (T) x (%)
4. Determine the number of discharge devices
• every 30 ft
N = (2L + 2W)/30
see 3.4
Aircraft Hangers
• omit
Truck Loading Rack
Truck Loading Rack
Hazards
Truck Loading Rack
Strategy
Truck Loading Rack
Design