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FT 32 FIRE FIXED INSTALLATION SYSTEM

NOT USING WATER (DCP) OBJECTIVE

1. To explain the function, operation and maintenance of dry chemical powder fire fixed installation system. REFERENCE

2. Manual of Fireman ship Book 9. CONTENTS

3. Introduction. A number of dry chemical extinguishing agents are now being used in portable extinguishers; fixed hand hose line systems and wheeled extinguishers some of these agents are currently available in also complete extinguishing systems. 4. Scope. This phase will cover the types dry chemical extinguishing systems, its

operation and maintenance 5. Types of Dry Chemical Agent and Application. The types of dry chemical agents available are:

a. Sodium Bicarbonate. It is the earliest, most popular dry chemical agent

because it is reliable, effective and economical. This agent is enhancing the flow of the powder. It is not compatible with protein foam, AFFF or detergent foams. Normally used in textile or cotton mills.

b. Foam-Compatible Type. It is basically sodium bicarbonate treated with

silicon to improve the flow. It is normally used for large-flammable liquid spills fires caused by aircraft crash. Te factors affecting foam compatibility are:

(1) The amount of physical disturbance of foam blanket.

(2) The characteristics of specific foam and dry chemical used in combination.

(3) The amount of dry chemical used.

(4) The rate of foam application.

c. Potassium Bicarbonate. Also known as ‘purple K’ is approximately two and

half times as effective as Sodium Bicarbonate on class B fires. It is not compatible with flour protein mechanical foam and AFFF. This chemical is extensively used to protect hydrocarbon fuels and typical class B situation.

d. Monoammonium Phosphate. Also known as ABC dry chemical agent used

in portable extinguishers. It is compatible with protein foam.

e. Potassium Chloride. Sometimes uses a trade name of ‘Super K’, is compatible with protein foams and has a high level of suppression efficiency.

f. Monet Powder. A dry chemical formulated from the product of potassium

bicarbonate and urea. It is compatible with protein foams and about six times more effective than sodium bicarbonate. It effectiveness many thousands of small particles smaller 0.01 macaronis size.

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g. Combustible Metal Dry Chemical. Consists mainly of potassium soleplate and is compatible with protein foam. Other additives are included to prevent moisture resistance and free-flowing properties. Normally used on combustible metals.

6. Extinguishing Effect of Dry Chemical Agents. Most dry chemical agents employ

similar extinguishing actions. Generally it is most effective when extinguishing flammable liquids fire involving hydrocarbon fuel spills. This type of situation requires cooling, smothering, radiation shielding and most important inhibiting or breaking the combustion chain reaction. 7. Basic System. The essential components of a dry chemical system which consists of:

a. A Actuation System. This consists of detectors and a manual means of

actuation, with or without remote stations. Such systems may utilize various type of detectors.

b. A Distribution System. This consists of piping and nozzles.

c. An Agent Container. This pressure vessel containing the selected agent with a appropriate means to expel the agent.

d. A Dry Chemical Agent. Now available are sodium bicarbonate, potassium

bicarbonate, monoammonium phosphate, potassium chloride and foam-compatible and combustible metal dry power. The following diagram shows a basic system.

Local application Using Overhead Nozzles

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8. The Theory Of Operation. The operation of the components a basic are as follows:

a. Dry Chemical Container:

(1) This normally a cartridge-operated and stores pressure type. A cylinder, charged normally is used to expel the chemical, keeps the dry chemical powder container under pressure. This design gives a faster response and discharge time.

(2) The pressurized-cylinder units have a bursting discharge so that the dry chemical cannot be discharged from the storage tank before the powder is properly fluidized. Dry powder must be under pressure to fluidized with gas,. In this manner the proper ratio of powder to gas is optimum for extinguishment.

300 Pound Cylinder Pressurized Dry Chemical Unit

Bursting Disc Installation

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(3) On actuation, pressurized gas is released into the powder container and the powder is discharged into the piping system. Normally 175 lbs of dry powder

can be discharged by nitrogen at 350 psi in 4.5 secs or 39 lbs/sec.

b. Distribution System:

(1) The system requires a piping system to distribute the fluidized dry chemical powder to the nozzles. The chemical may reach a high speed of 7500 ft/min exerting tremendous force of the bends and joints of the piping system.

(2) Venture assemblies are normally fitted before ‘T’ fittings to ensure remixing of powder before dividing.

9. Types of Dry Chemical Extinguishing Systems. There are basically 3 type:

a. Total flooding system. b. Local application system. c. Pre-engineered system.

10. Total Flooding System. Total flooding system can be used to distribute dry chemical throughout an enclosure when the areas of enclosure sides, ceiling and floor. Although dry chemical powders are non-toxic, they do not displace oxygen, it will obscure vision and create temporary breathing difficult due to this pre-discharge alarms will have to be provided. 11. The system also incorporates electro-mechanical procedures to close windows, doors and other openings; switches to turnoff ventilation system and exhaust fans. A typical total-flooding system of a cylinder-pressure type is seen at the following diagram. 12. These systems are normally activated automatically by detection systems but may also have remotely located manual devices. 13. The nozzle of this system are located at the highest point of the enclosure. There are symmetrically laid out for essential uniform dry chemical discharge from all nozzles.

Total Flooding Dry Chemical System

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14. Local Application systems. This system is designed to discharge agents directly or to hazardous equipment, process or apparatus. The following diagram shows a typical layout for a dip tank. 15. This system may be used on interior or exterior hazards. When used outdoors, the rate and duration of discharge may have be adjusted for adverse wind conditions. Common use for this system is the protection of electrical hazards – high voltage transformer. 16. Per-Engineered System. This system is intended for hazard situations that are of

similar configuration with a variation in the size of unit. It is most widely and successfully used in restaurants and institutional kitchens. Fusible detection and link detection/actuation arrangement as well a manual release control. 17. Selector Valve Arrangement. Larger systems can be equipped with a selector arrangement making it possible to provide:

a. Hand hose lines. b. Protect more than one hazard in isolation by different piping.

18. In this arrangement it is important to separate hazards by distance or structure to prevent heat of fire from one hazard activating the system for any other hazards. 19. Hand hose line systems may involve a hose and control nozzle using dry chemical from a separate supply. Dual agent types i.e. with AFFF can also be used. 20. Maintenance. The following maintenance tasks are to be carried out:

a. Endure that the stored-pressure unit must be completely leak-proof. b. Ensure that the dry chemical container has a bursting disc. c. All piping systems must be secure.

Local Application Using Tankside Nozzles