fire detection and suppression chapter 3 water supply

Fire Detection and Suppression

Chapter 3

Water Supply

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Characteristics of Water

• Compound of two parts hydrogen and one part oxygen (H20)

— Liquid between 32F and 212F (0C and 100C)

— Solid below 32°F (0C)

— Gas above 212°F (100°C)

• Incompressible

• Weight for fire protection purposes=62.5 lb/ft3 or 8.33 lb/gal (1 kg/L)

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Extinguishing Properties of Water

• The law of specific heat: the specific heat of any substance is the ratio between the amount of heat needed to raise the temperature of a specified quantity of a material and the amount of heat needed to raise the temperature of an identical quantity of water by the same number of degrees.

(Continued)

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Extinguishing Properties of Water (cont.)

• The law of latent heat of vaporization— The latent heat of vaporization is the quantity of

heat absorbed by a substance when it changes from a liquid to a vapor.

— 1 gallon of water will absorb 9,346 Btu (1,266 + 8,080) of heat if all the water is converted to steam.

(Continued)

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• Surface area of water: the speed with which water absorbs heat increases in proportion to the water surface exposed to the heat.— Expansion ability

— Smothering ability(Continued)

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• Specific gravity: the density of liquids in relation to water — Liquids with a specific gravity less than 1 are

lighter than water and therefore float on water.

— Most flammable liquids have a specific gravity of less than 1.

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Water’s Advantages as an Extinguishing Agent

• Greater heat-absorbing capacity

• Large amount of heat required to change water into steam

• Easily expanded surface area

• Plentiful supply

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Water’s Disadvantages as an Extinguishing Agent

• High surface tension

• Reactivity

• Low levels of opacity and reflectivity

• Freezes at 32F (0C)

• Conductivity

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Water Pressure and Velocity

• Pressure: force per unit area on a liquid or gas expressed in psi or kPa

• Force: simple measure of weight

• Velocity— The speed at which fluid travels through hose or

pipe

— Result of pressure exerted on the fluid at its source

(Continued)

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Water Pressure and Velocity (cont.)

• Principles of pressure— First Principle: fluid pressure is perpendicular to

any surface on which it acts.

— Second Principle: fluid pressure at a point in a fluid at rest is the same intensity in all directions.

— Third Principle: pressure applied to a confined fluid from without is transmitted equally in all directions.

(Continued)

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• Principles of pressure— Fourth Principle: the pressure of a liquid in an

open vessel is proportional to its depth.

— Fifth Principle: the pressure of a liquid in an open vessel is proportional to the density of the liquid.

— Sixth Principle: the pressure of a liquid on the bottom of a vessel is independent of the shape of the vessel.

(Continued)

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• Types of pressure— Atmospheric pressure: pressure exerted on the

earth by the atmosphere itself

— Head pressure– Height that a pressure can lift a column of liquid

– Height of a water supply above the discharge orifice is called the elevation head.

— Static pressure: stored potential energy available to force water through pipe, fittings, fire hose, and adapters

(Continued)

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Water Pressure and Velocity • Types of pressure (cont.)

— Normal operating pressure: pressure found in a water distribution system during normal consumption demands

— Residual pressure: that part of the total available pressure not used to overcome friction loss or gravity while forcing water through pipe, fittings, fire hose, and adapters

— Flow pressure (velocity pressure): forward velocity pressure while water is flowing

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Pressure Loss and Gain• Elevation

— Center line of the pump or the bottom of a static water supply source above or below ground level

— Elevation pressure results from differences in elevation of nozzle and pump.

• Altitude— Position of an object above or below sea level

— Effects of lower atmospheric pressure on drafting above 2000 feet (600 m)

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Friction Loss

• That part of the total pressure lost while forcing water through pipe, fittings, fire hose, and adapters

(Continued)

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Friction Loss (cont.)

• Causes— Movement of water molecules against each other

— Linings in fire hose/inside surface of piping

— Hose couplings/pipe fittings

— Sharp bends

— Change in hose size or in orifice by adapters

— Improper hose-coupling gasket size/pipe control valves

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Friction Loss (cont.)

• Principles of friction loss:— First principle: if all other conditions are the same, friction

loss varies directly with the length of the hose or pipe.

— Second principle: when hoses are the same size, friction loss varies approximately with the square of the increase in the velocity of the flow.

— Third principle: for the same discharge, friction loss varies inversely as the fifth power of the diameter of the hose.

(Continued)

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Friction Loss

• Principles of friction loss (cont.):— Fourth principle: for a given flow velocity, friction

loss is approximately the same, regardless of the pressure on the water.

• Other factors affecting friction loss: diameter and length of hose or pipe

• Reducing friction loss

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Water Hammer

• Energy surge that results from suddenly stopping or starting water moving through hose or pipe

• Can damage the pump, appliances, hose, or the municipal water system itself

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Municipal Water Supply Systems

• Components— Source of water supply

— Means of moving water

— Water processing or treatment facilities

— Water distribution system, including storage(Continued)

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Municipal Water Supply Systems (cont.)

• Sources of water supply— Public water supply system

— Surface or ground water

• Means of moving water— Directing pumping system

— Gravity system

— Combination system(Continued)

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• Water processing or treatment facilities— The fire department’s main concern regarding

treatment facilities is that a maintenance error, natural disaster, loss of power supply, or fire could drastically reduce the volume and pressure of water available for fire fighting operations.

(Continued)

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• Water Distribution System— Dead-end hydrants

— Circulating feed or looped lines

— Grid system– Primary feeders

– Secondary feeders

– Distributors

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Water Distribution System Variables

• Piping materials

• Pipe diameter

• Piping arrangement— Simple loop

– One inflow point and one outflow point.

– Exactly two paths between the inflow and outflow points.

(Continued)

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• Piping arrangement (cont.)— Complex loop (grid)

– More than one inflow point

– More than one outflow point

– More than two paths between inflow and outflow points

(Continued)

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• Piping arrangement (cont.)— Valves

– Function in system

– Location in system

– Access

– Indicating

– Nonindicating

– Gate valves

– Butterfly valves(Continued)

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• Piping arrangement (cont.)— Hydrants

– Dry-barrel and wet-barrel

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• Piping arrangement (cont.)– Distribution and location

– Maintenance

– Color coding:

Less than 500 gpm: Red

500999 gpm : Orange

1,0001,499 gpm: Green

1,500 gpm or more: Light Blue

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Private Water Supply Systems

• Purposes— To provide water strictly for fire protection

purposes

— To provide water for sanitary and fire protection purposes

— To provide water for fire protection and manufacturing processes

• Potential problems for fire fighting purposes(Continued)

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Private Water Supply Systems (cont.)

• Water supply requirements for standpipe and hose systems— NFPA 14, Standard for the Installation of

Standpipe and Hose Systems

— Class I service

— Class II service

— Class III service(Continued)

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Private Water Supply Systems (cont.)

• Water supply requirements for automatic sprinkler systems— NFPA 13, Standard for the Installation of

Sprinkler Systems

— Pipe schedule systems

— Hydraulically designed water-based extinguishing systems

(Continued)

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Private Water Supply Systems

• Water supply requirements for automatic sprinkler systems (cont.)— Duration of water supplies

– See Table 3.5 in manual

– NFPA 231, Standard for General Storage

fire detection and suppression chapter 3 water supply

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