Low Expansion Foam NFPA 11 class B –flammable liquids, FP < 100 0 F –combustible liquids FP...

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