8

Offensive

Operations

8

Learning Objectives (1 of 15)

• Compare an offensive fire attack to a

defensive fire attack, explaining the

basics of each type of attack and

identifying the rationale for each

strategy.

• Describe trial-and-error methods of

calculating rate of flow.

8

Learning Objectives (2 of 15)

• Explain the theory of indirect

extinguishment.

• Compare conditions within a fire

compartment after pulsing versus after

an indirect attack.

8

Learning Objectives (3 of 15)

• Analyze rate-of-flow requirements using

V/100, A/3, and sprinkler calculations.

• Define a ventilation-controlled fire.

• Define a fuel-controlled fire.

8

Learning Objectives (4 of 15)

• Describe “area of involvement” and how

it applies to rate-of-flow calculations.

• Write a brief position paper outlining the

advantages of using the Royer/Nelson

(V/100) rate-of-flow formula.

8

Learning Objectives (5 of 16)

• Explain why a fire attack meeting or

exceeding the calculated rate of flow

could fail to extinguish the fire.

• Explain the relationship between nozzle

type, rate of flow, and nozzle reaction

force.

8

Learning Objectives (6 of 15)

• Discuss the advantages and

disadvantages of using an aerial device

as a portable standpipe.

• Describe extinguishment of ordinary

combustibles by inhibiting pyrolysis.

8

Learning Objectives (7 of 15)

• Discuss the dangers of opposing fire

streams and ways to avoid opposing fire

streams.

• Define external exposure.

• Define internal exposures.

• List factors to consider when evaluating

external exposures.

8

Learning Objectives (8 of 15)

• Describe the purpose of a backup line

and how it can be used to protect fire

fighters attacking the fire.

• Evaluate water supply requirements

based on rate of flow and other factors.

8

Learning Objectives (9 of 15)

• Examine the relationship and proper

use of ventilation during offensive

extinguishment operations.

• Describe the factors that determine the

number of apparatus needed at an

offensive operation.

8

Learning Objectives (10 of 15)

• Discuss apparatus management at a

medium- to large-scale incident.

• Develop a list of advantages and

disadvantages when using Class A

foam during structural firefighting.

8

Learning Objectives (11 of 15)

• Compute and compare the rate of flow

for various areas using A/3 and V/100.

• Evaluate the available flow from

standard pre-connected hose lines and

determine when the rate of flow for a

structure should be pre-incident

planned.

8

Learning Objectives (12 of 15)

• Estimate the number and size of hose

lines needed to apply a calculated rate

of flow.

• Assess staffing requirements for an

offensive attack based on rate-of-flow

and life safety factors.

8

Learning Objectives (13 of 15)

• Assess the probability of an imminent

life-threatening situation.

• Compare staffing available to staffing

requirements.

8

Learning Objectives (14 of 15)

• Using a fire scenario, assess the total

water supply available and apparatus

needs in terms of required fire flow.

• Given fire conditions and location,

determine the ventilation possibilities

and choose the best ventilation

method(s).

8

Learning Objectives (15 of 15)

• Evaluate the flow available from a standpipe system and standard fire department standpipe equipment based on a calculated rate of flow.

• Examine and evaluate various attack positions in a multi-story building.

• Discuss factors involved in choosing an offensive strategy.

8

Overview

• Offensive versus defensive fire attack

– Based on staffing levels and risk–benefit

analysis

• Rate-of-flow

– Determines number and size of hose lines

• Resource capabilities must meet

incident requirements

8

Calculating Rate of Flow

• Methods

– Clark’s calculation

– Trial and error

– Royer/Nelson formula

– National Fire Academy formula

– Sprinkler calculations

• Cannot predict every variable

8

Indirect Application

• Lloyd Layman

– Coast Guard tests

– Based on water converting to steam

– Reduced water use = less property

damage

– Disrupts heat balance

• Decreases chances for occupant survival

• Increases chances for fire fighter steam burns

8

Royer/Nelson Formula (1 of 2)

• V/100 = Volume in cubic feet divided by

100

• Oxygen controlled fires

– Require less water

• Valid for most fires

– Accounts for ceiling heights

• Recommended for pre-planning

8

Royer/Nelson Formula (2 of 2)

8

NFA Formula (1 of 2)

• A/3 = Area in square feet divided by 3

• More conservative and less accurate

• Yields a higher rate of flow in most

situations

• Recommended for scene use

8

NFA Formula (2 of 2)

8

Sprinkler Calculations (1 of 2)

• Most accurate

• Considers fuel load and type

• Useful in pre-planning

• Published in NFPA documents and

Factory Mutual Data Sheets

• NFPA 13: Standard for the Installation

of Sprinkler Systems

8

Sprinkler Calculations (2 of 2)

• Variables:

– Building type

– Number of floors

– Occupancy type

– Commodity inside the structure

– Storage configuration of the commodity

8

Stages of Fire

• Early stages: fuel dependant

• Late stages: oxygen dependant

• Well involved fires controlled by both

• Once ventilated, fire reacts to type and

amount of fuel.

8

Estimating Compartment Size

• Rate-of-flow based on area or volume of

compartment(s) on fire

• Calculating each area separately is

recommended.

– Provide flow needed for largest area.

• Fire fighters can estimate size for IC.

8

Pre-Planning by Occupancy

• One- and two-family dwellings

• Apartment buildings

– Common areas

• Small businesses

8

Estimating Percent of Area on

Fire

• Royer/Nelson

– Volume of enclosure

– Doesn’t consider modifying formula

• NFA

– Area of involvement

– Percentage-of-involvement modifier

recommended

8

Comparing Rate-of-Flow

Calculations (1 of 2)

• Sprinkler calculations, variables:

– Building type

– Number of floors

– Occupancy type

– Commodity

– Storage configuration

• Most accurate

• Based on actual fire experience

8

Comparing Rate-of-Flow

Calculations (2 of 2)

• U.S. National Fire Academy system

– Yields higher rate of flow

– Field-estimated

– Overestimation leads to quicker

extinguishment with less water

– Gross overestimation may cause a delay in

attack

8

Which Rate-of-Flow

Calculation Is Best?

• Each method has merit.

• If fuel load is heavy, sprinkler

calculations should be used.

• A/3 formula may be easier, but may not

be as accurate.

• Each formula must be modified based

on trial and error.

8

Selecting Attack Hose Size

• Booster hose inappropriate for structure fires

• 1¾” (44-mm) attack hose lines recommended as a minimum

– With backup hose line, will be adequate to extinguish most fires

• Mobility decreases, flow increases with 2½” (64-mm)

8

Nozzle Flow Rates

• Flow rates vary according to:

– Nozzle pressure

– Pump discharge pressure

– Length of hose lay

8

Nozzle Flow Ratings

• Variable-stream nozzles rated by:

– Pump discharge pressure and the length of

hose, or

– Nozzle pressure

• Smooth-bore nozzles rated by:

– Nozzle pressure

8

Nozzle Pressure

8

Nozzle Reaction Force

• Increases as the flow and nozzle

pressure increase

• Makes nozzle more difficult to control

• If reaction force is too great:

– Flow should be reduced

– Nozzle should be replaced with one that is

easier to control

8

Portable Standpipes

• Aerial ladder

– Limited to height of ladder

• Pre-piped waterway

• Pressures supplied by apparatus pumps

– Eliminates potential standpipe problems

• Can be used in buildings not standpipe equipped

8

Nozzle Selection

• Variable-stream versus smooth bore

• Stream force

– Affects the distance the stream will carry

– Allows the crew to access hidden fires

• Fog streams

– Stop forward extension of fire

– Provide exposure protection

8

Selecting Stream Position (1 of 3)

• Indirect attack

– Little application to structural firefighting

– Steam production is dangerous

• Poor choice in occupied areas

– Useful in unoccupied basements, attics, or

storage areas

– Piercing nozzles

8

Selecting Stream Position (2 of 3)

• Direct attack

– Preferred

– Applies water directly on the burning

material

• Reduces temperature of the fuel

• Reduces or eliminates combustible vapors

8

Selecting Stream Position (3 of 3)

• Combination attack

– Direct and indirect application

– Dangerous for interior application

• Disturbs heat balance

• Generates intense steam

8

Direct Attack

8

Combination Attack

8

Hose Line Placement

• Risk-versus-benefit analysis

• First line should be placed between the

victim and the fire.

– Coordinated with entry and ventilation

• Objective is to get water directly on the

fuel.

8

Number of Attack Lines

• Based on flow requirements

• A single 1¾” (44-mm) hose line for most

dwelling fires

• Backup hose line

– Protects egress routes

– Bolsters attack

8

Evaluating Exposures

• Internal

– Natural pathways

• Concealed spaces, stairs, chutes, and shafts

• Vertically up the exterior of the building from

windows or other openings

8

External Exposures (1 of 2)

• Adjacent buildings

• Improper ventilation can expose

buildings.

• Consider fire apparatus and equipment

parked near the fire building.

8

External Exposures (2 of 2)

8

Factors to Consider

• Proximity to the fire building

• Wind direction

• Height of exposure

• Life hazard in the exposure

• Hazard presented by the exposed

occupancy

8

Backup Lines

• Protect the crew on the initial attack line

– Also provide additional flow if needed

• At least as large as the initial attack line

8

Additional Lines

• To meet the rate of flow in the

immediate fire area

• Backup hose line(s) for immediate fire

area

• To protect egress routes

• To protect internal/external exposures

• Other backup hose lines as needed

8

Water Supply Needs

• Large diameter hose effective

• Two supplies recommended

• Shouldn’t rely solely on water tank

supply

• Must supply calculated rate-of-flow

– Plus backup/exposure lines

8

Ventilation Needs

• Used to assist in extinguishment efforts

– Allows approach to fire

– Controls fire spread

– Makes conditions tenable

• Venting to support extinguishment

– Timing is crucial

– Charged lines must be in place

• Improper venting can extend fire

8

Staffing Needs

• Based on:

– Rate of flow

– Backup lines

– Placement of lines above the fire

– Secondary water supply

8

Initial Response

• NFPA 1710

– Defines tasks and minimum staffing for the

initial response

– If needs not met, must call for mutual aid or

additional alarms

8

Apparatus Needs

• Normally sufficient for initial response to offensive operation

• Proper positioning crucial

• Use only those necessary to meet tactical objectives.

• Large scale incident or staging area – Staging officer

– Staged apparatus: staffed

– Out of service apparatus: not staffed

8

Class A Foam (1 of 2)

• Wildland and wildland/urban interface

uses:

– Pre-wetting fuels

– Providing a foam layer on an exposure

• Reduces radiant heat absorption

– Suppression agent

– Wetting agent

• Resulting in greater penetration

8

Class A Foam (2 of 2)

• Useful in areas with a marginal water

supply

• Less water damage because less water

is used

8

Summary

• Considerations for a safe and effective

offensive operation

– Sufficient personnel and resources:

• to deliver the required rate of flow

• to protect the fire fighters

• Rate-of-flow formulas

– Most valuable when included in pre-plans

– V/100 or sprinkler charts used in pre-plans