Fire Science and Suppression Fundamentals

Introduction

Fire suppression is most effective when it is based on an understanding of how fire starts, develops, transfers heat, and can be controlled. Fire is not simply a flame; it is a rapid, self-sustaining chemical reaction involving fuel, an oxidizing agent, heat, and an uninhibited chain reaction. Suppression systems are designed to interrupt one or more of these conditions while protecting people, property, and continuity of operations.

For fire and safety professionals, fire science provides the foundation for selecting extinguishing agents, locating detection and suppression equipment, estimating fire severity, interpreting fire classes, and recognizing the limitations of automatic and manual systems. A system that is suitable for a computer room may be unsuitable for a deep-fat fryer, a warehouse, or an energized electrical installation.

This chapter introduces the fundamental principles needed to understand those decisions.

Learning Objectives

By the end of this chapter, the learner should be able to:

1. Explain combustion and distinguish complete from incomplete combustion.
2. Describe the fire triangle and fire tetrahedron.
3. Explain conduction, convection, radiation, and mass transport as mechanisms of fire spread.
4. Identify the stages of fire growth and the significance of flashover and backdraft.
5. Classify fires and select appropriate broad categories of extinguishing agents.
6. Explain cooling, smothering, starvation, dilution, and chemical inhibition.
7. Describe fire load and use simple fire-load calculations.
8. Evaluate the principal limitations of suppression methods.
9. Apply fire-science principles to a practical suppression-system decision.

1. Combustion: The Chemical Basis of Fire

Combustion is a chemical oxidation reaction that releases heat and often produces light. In ordinary fires, a carbon-containing fuel reacts with oxygen in air. A simplified complete-combustion reaction for a hydrocarbon fuel is:

Here, CₓHᵧ represents a hydrocarbon fuel, O₂ is oxygen, CO₂ is carbon dioxide, and H₂O is water vapour. This equation is an idealized representation. Real fires commonly involve many intermediate reactions, incomplete mixing, variable temperatures, and changing oxygen concentrations.

Complete combustion occurs when fuel is adequately mixed with sufficient oxygen and reaches an appropriate temperature. It tends to produce carbon dioxide, water vapour, and relatively little smoke. Incomplete combustion occurs when oxygen is insufficient, mixing is poor, or the temperature is too low. It can produce carbon monoxide, soot, unburned hydrocarbons, and other toxic products.

The visible flame is a region in which gaseous fuel or vapour reacts with an oxidizer. Solids do not usually burn directly as solid blocks. They first undergo pyrolysis: heat decomposes the solid and releases combustible vapours. These vapours mix with air and burn above the surface. Plastics, wood, textiles, and many synthetic materials therefore produce flames through the burning of pyrolysis gases.

Liquids burn in a similar indirect manner. The liquid must evaporate sufficiently to produce a vapour concentration within its flammable range. The temperature at which a liquid produces enough vapour to form an ignitable mixture near its surface is related to its flash point. A low flash point generally indicates a greater likelihood of ignition at ordinary temperatures.

Essential combustion conditions

Combustion requires:

• a combustible fuel;
• an oxidizer, normally oxygen in air;
• sufficient heat to reach ignition conditions; and
• continuing chemical reactions that sustain the process.

Removing any one of these conditions can stop flaming combustion. However, extinguishment is not always permanent. A fuel may reignite if residual heat remains or if vapours continue to be generated.

2. The Fire Triangle and Fire Tetrahedron

The traditional fire triangle represents three requirements for fire: fuel, oxygen, and heat. It is useful for introductory explanation, but it does not fully represent the chemistry of flame propagation.

The fire tetrahedron adds the fourth element: an uninhibited chemical chain reaction. This model is particularly useful when explaining dry-chemical extinguishing agents, which may interrupt flame chemistry without primarily cooling the fuel.

The four elements

Fuel. Fuel may be solid, liquid, gas, or vapour. Its physical form, surface area, volatility, moisture content, and arrangement influence fire behaviour.

Oxygen or oxidizer. Most fires use atmospheric oxygen, which is approximately 21% by volume in normal air. Some substances can burn in oxygen-rich environments, and a few chemicals contain oxygen or another oxidizing component within their own structure.

Heat. Heat raises fuel to ignition temperature, causes evaporation or pyrolysis, and maintains the reaction. Heat may remain after visible flames disappear.

Chemical chain reaction. Combustion involves reactive species such as free radicals. Chain reactions include initiation, propagation, branching, and termination steps. Agents that interfere with these reactions can suppress flames rapidly.

A suppression action can therefore be interpreted as removing or weakening one or more tetrahedron elements. Water mainly removes heat; foam separates fuel from air and may also provide cooling; carbon dioxide dilutes oxygen and provides limited cooling; dry chemical interrupts chain reactions and separates the flame from the fuel surface.

3. Heat Transfer and Fire Spread

Fire growth depends on how heat moves. The four major mechanisms are conduction, convection, radiation, and mass transport.

Conduction

Conduction is heat transfer through a material or between materials in direct contact. Metals are generally good conductors, while many insulating materials conduct heat poorly. A steel beam heated in one compartment may transfer heat to another area and ignite nearby combustibles or weaken structural members.

For one-dimensional steady conduction through a uniform layer, the heat-transfer rate can be represented by Fourier’s law:

where q̇ is heat-transfer rate in watts, k is thermal conductivity in W/(m·K), A is area in m², ΔT is temperature difference in K, and L is conduction distance in m. This simplified expression assumes steady conditions, uniform material properties, one-dimensional heat flow, and negligible internal heat generation. Fire conditions are often transient, so the equation is mainly useful for conceptual analysis rather than direct fire prediction.

Convection

Convection transfers heat through the movement of fluids, including air and smoke. Hot gases rise because heated gases become less dense than surrounding cooler gases. A ceiling layer can spread rapidly across a compartment and preheat combustibles remote from the initial fire. Mechanical ventilation, wind, shafts, stairwells, and open doors can strongly alter smoke and heat movement.

Natural convection is driven by buoyancy. Forced convection is produced by fans, pressure differences, or airflow through openings. Suppression and ventilation strategies must be coordinated: ventilation can remove smoke, but it can also supply oxygen and intensify burning if introduced at the wrong time.

Radiation

Radiation transfers energy through electromagnetic waves and does not require direct contact or a moving fluid. Flames, hot smoke layers, walls, and heated equipment radiate energy to nearby surfaces. Radiation is important in large fires, warehouses, fuel spills, and situations where adjacent objects are separated by an air gap.

Radiant heat exposure may ignite a material after it has been heated for a period, even if the material is not touched by flame. Water sprays can reduce radiant exposure by cooling surfaces and, in some arrangements, attenuating radiant energy.

Mass transport

Fire spread also involves movement of fuel vapours, smoke, oxygen, embers, and burning droplets. Burning brands can travel through air and ignite roofs or vegetation. Leaking flammable liquids can spread fire beyond the original source. Smoke movement can transport toxic gases and heat to occupants far from the seat of fire.

4. Fire Growth and Compartment Behaviour

A fire typically progresses through several recognizable stages, although real fires do not always follow them neatly.

Incipient stage

The incipient stage begins with ignition and localized burning. Heat release is relatively small, but smoke and toxic gases may already be hazardous. Early detection and prompt intervention are highly valuable during this stage.

Growth stage

During growth, the flame spreads to additional fuel and the heat-release rate increases. A hot smoke layer forms near the ceiling and descends as more gases accumulate. Radiant and convective heating precondition other combustible surfaces.

Flashover

Flashover is a rapid transition in which most exposed combustible surfaces in a compartment become involved in flaming combustion. It is associated with a severe increase in heat release and is a critical life-safety hazard. Flashover is not a fixed-temperature event in every compartment; it depends on ventilation, fuel arrangement, enclosure geometry, and thermal conditions.

Fully developed stage

In the fully developed stage, the available fuel or ventilation controls the burning rate. A well-ventilated fire may produce extreme temperatures and structural damage. A ventilation-limited fire may contain large quantities of hot, fuel-rich gases but burn less vigorously until an opening supplies oxygen.

Decay stage

The decay stage occurs when fuel or oxygen is depleted, or when suppression reduces the heat-release rate. Dangerous conditions may remain. Smouldering materials can reignite, and opening a compartment can introduce oxygen suddenly.

Backdraft

A backdraft is a potentially explosive or rapidly escalating event caused by the introduction of air into a compartment containing hot, oxygen-deficient, combustible gases. Indicators may include dense smoke, pressurized smoke movement, limited visible flame, and unusually hot doors or surfaces. Recognition requires training and should never replace established incident-command and entry procedures.

5. Fire Classes and Fuel Characteristics

Fire classifications vary somewhat by jurisdiction and standard. The following categories are widely used in fire-safety education, but local legislation and equipment markings must always be followed.

Classification is a communication tool, not a complete hazard assessment. The same occupancy may contain several fuel types. For example, a commercial kitchen may have cooking oil, paper packaging, LPG, electrical equipment, and ordinary combustibles.

6. Extinguishing Mechanisms

Cooling

Cooling reduces the temperature of the fuel or surrounding materials below the level required for sustained vapour production and combustion. Water is highly effective on many Class A fires because it absorbs substantial heat when raised to its boiling point and converted to steam.

The energy required to heat and vaporize water can be approximated by:

where Q is energy absorbed in joules, m is water mass in kilograms, c is specific heat capacity in J/(kg·K), ΔT is temperature rise in K, and Lᵥ is latent heat of vaporization in J/kg. This expression assumes that the water reaches the boiling point and then vaporizes; in practice, only part of the applied water may participate effectively, and heat losses occur.

Worked example: If 2 kg of water is heated from 20 °C to 100 °C and vaporized, using c ≈ 4.18 kJ/(kg·K) and Lᵥ ≈ 2257 kJ/kg:

Q = 2 × 4.18 × 80 + 2 × 2257 ≈ 5,183 kJ.

This illustrates why water can absorb considerable heat. It does not mean that every 2 kg applied to a fire removes exactly this amount, because application efficiency, runoff, steam movement, and fire geometry matter.

Smothering and oxygen exclusion

Smothering separates the fuel from air or reduces oxygen concentration near the flame. Foam blankets flammable-liquid surfaces, reducing vapour release and preventing contact with air. A fire blanket can cover a small flame. Carbon dioxide displaces air locally, especially in enclosed spaces.

Smothering is less reliable in open, windy environments. It may also fail if the fuel continues to evaporate or if the agent disperses before a stable barrier is established.

Starvation

Starvation removes the fuel or prevents it from reaching the combustion zone. Examples include closing a fuel valve, stopping a pump, isolating a process line, removing nearby combustibles, and controlling leakage. Fuel isolation is often essential for gas and liquid-fuel fires because extinguishing the flame without stopping the leak can create an unignited, explosive cloud.

Dilution

Dilution reduces the concentration of oxygen or fuel vapour below the flammable range. Inert gases such as nitrogen or carbon dioxide may be used in designed systems. Water can dilute some water-miscible liquids, but this is highly substance-dependent and should not be assumed for unknown chemicals.

Chemical inhibition

Some dry-chemical agents interrupt flame-propagating reactions. They can extinguish flames rapidly, but their cooling capacity may be limited. Deep-seated fires can therefore reappear after the visible flame is removed. Dry chemical residue may damage sensitive equipment and contaminate food-processing areas.

7. Suppression Agents and System Applications

Water systems

Water is commonly delivered through hose reels, hydrants, sprinklers, water spray, or water mist. Sprinklers control or suppress many developing fires by applying water automatically to the region of rising heat. They do not guarantee extinguishment of every fire, and their performance depends on correct design, water supply, spacing, obstruction control, maintenance, and hazard classification.

Water can be unsuitable or dangerous where it reacts with chemicals, spreads burning liquids, conducts electricity under particular conditions, or causes unacceptable damage. Water mist uses small droplets with high surface area and can provide cooling and local oxygen displacement, but performance is system-specific.

Foam systems

Foam forms a blanket over certain flammable-liquid surfaces. Important performance factors include foam type, expansion ratio, drainage characteristics, fuel compatibility, application method, and environmental requirements. Foam must be applied gently enough to avoid plunging into the fuel and causing splashing.

Carbon dioxide systems

Carbon dioxide is electrically nonconductive and leaves little residue, making it useful in selected machinery and process hazards. It presents a severe life-safety hazard because it can reduce oxygen concentration and impair consciousness. Total-flooding systems require enclosure integrity, pre-discharge alarms, time delays, evacuation, lockout controls, and procedures preventing re-entry until the atmosphere is confirmed safe.

Clean-agent systems

Clean agents are gaseous or volatile agents designed to leave little residue. They may suppress fire through heat absorption, chemical inhibition, or both. They are often considered for occupied or sensitive areas, but concentration, enclosure integrity, agent decomposition products, environmental impact, personnel exposure limits, and maintenance requirements must be evaluated.

Dry chemical systems

Dry chemical systems are effective for many rapidly developing flame fires, including selected flammable-liquid and gas hazards. They provide fast flame knockdown but limited post-fire cooling. Reignition, residue, visibility reduction, respiratory exposure, and equipment contamination are important concerns.

Wet chemical systems

Wet chemical systems are designed especially for commercial cooking hazards. The agent reacts with hot cooking oils to form a soap-like surface layer, a process commonly called saponification, while also cooling the fuel. Correct nozzle placement, fuel type, duct protection, automatic fuel shutoff, manual activation, and regular cleaning are essential.

8. Fire Load and Potential Fire Severity

Fire load is the quantity of combustible material available in a space, expressed in terms of energy or an equivalent mass of a reference fuel. It is not the same as the actual heat released in a fire. Actual heat release depends on ventilation, arrangement, burning efficiency, suppression, and the fraction of fuel that becomes involved.

A basic total fire-load estimate is:

where E_f is potential chemical energy in joules, mᵢ is the mass of combustible material i in kilograms, and Hᵢ is its effective heat of combustion in J/kg. If a floor area is used, fire-load density is:

where q_f is fire-load density in J/m² and A is the relevant floor or compartment area in m². The selected area must be stated because using the entire building area or only the burning zone produces different interpretations.

Worked example: A 100 m² room contains 500 kg of material with an effective heat of combustion of 16 MJ/kg. Then:

E_f = 500 × 16 = 8,000 MJ.

The average fire-load density is:

q_f = 8,000/100 = 80 MJ/m².

This is a potential-energy estimate, not a prediction that 8,000 MJ will be released at once. For design, recognized codes and engineering methods may use more detailed fuel distributions, design fires, ventilation assumptions, and sprinkler response criteria.

Fire load affects the expected duration, heat exposure, smoke production, structural demand, and suppression-water requirements. High storage arrangements can create deep-seated fires that continue after surface flames are controlled.

9. Limitations of Suppression Methods

No extinguishing agent is universally safe or effective. Key limitations include:

• Reignition: Residual heat or continued vapour generation can restart combustion.
• Hidden fire: Fire may spread inside walls, ceilings, insulation, ducts, voids, or storage piles.
• Limited reach: A portable extinguisher may not penetrate a large or shielded fire.
• Ventilation effects: Opening doors or activating fans can intensify a ventilation-limited fire.
• Agent incompatibility: Water, foam, dry powder, and gaseous agents each have hazards for particular fuels.
• Supply limitations: Systems may lose effectiveness because of inadequate pressure, blocked piping, empty cylinders, frozen water, or impaired pumps.
• Obstructions: Racking, beams, suspended ceilings, and equipment can prevent agent distribution.
• Human factors: Delayed alarm, poor training, panic, incorrect extinguisher selection, and unsafe approach can defeat a technically adequate system.
• Environmental and health effects: Some agents create toxicity, oxygen-deficiency, residue, corrosion, noise, or environmental burden.
• Structural collapse: Suppression does not remove the risk of collapse in a heated structure.

Suppression is therefore one part of a broader fire-safety strategy involving prevention, compartmentation, detection, alarm, evacuation, emergency planning, passive protection, inspection, testing, and maintenance.

10. Applied Case: Illustrative Warehouse Fire

Background

Consider an illustrative 1,200 m² warehouse storing boxed plastic components on six-metre-high racks. The building has automatic sprinklers, smoke detection, hydrants, and a fire pump. A charging area for battery-powered equipment is located near one wall.

Problem

A forklift damages packaging and ignites combustible materials near the rack face. Employees initially use a portable water extinguisher but withdraw when smoke increases. The fire grows vertically and begins heating the ceiling layer.

Analysis

The fuel is principally Class A combustible solids, but plastic packaging may produce high heat release and dense toxic smoke. The rack arrangement creates vertical channels that can accelerate flame spread. The warehouse height and storage configuration require sprinkler design appropriate to the commodity and storage arrangement; ordinary office sprinklers cannot automatically be assumed adequate.

The water extinguisher provides cooling but may not reach burning materials deeper in the rack. Detection and sprinkler activation are valuable because early control limits heat release before widespread involvement. Smoke movement may threaten occupants before flames reach the entire building.

Approach and solution

The emergency plan should require immediate alarm activation, evacuation, notification of the fire service, and only trained intervention with a clear escape route. The sprinkler system should be inspected for correct valve position, adequate water supply, and obstructions. Storage should maintain required clearances below sprinklers and should not exceed the approved commodity classification.

Fire-service operations may include controlling exposures, checking for concealed fire, isolating energy sources where safe, and using thermal imaging and overhaul procedures after visible flames are controlled. The charging area should be assessed separately for electrical and battery-related hazards.

Outcome

If the sprinkler system operates as designed and the fire is detected early, the likely outcome is control of the fire to a limited rack area, reduced structural exposure, and improved evacuation time. If sprinklers are obstructed or the storage arrangement exceeds the design basis, suppression may be delayed or ineffective, allowing flashover-like conditions within the rack or compartment.

Learning points

1. Fuel classification must include the arrangement and depth of storage, not merely the material name.
2. Suppression performance depends on design assumptions and maintenance.
3. Water may control a surface fire without immediately extinguishing a deep-seated fire.
4. Detection, alarm, evacuation, and suppression work as an integrated system.
5. Firefighters and occupants must consider smoke and structural hazards, not only visible flame.

11. Professional Practice, Regulation, and Emerging Developments

Fire suppression work must comply with applicable national building regulations, fire codes, occupational-safety requirements, product approvals, and recognized installation and inspection standards. Exact requirements vary by jurisdiction. Competent persons should use the current edition of the applicable standard and consult the authority having jurisdiction.

Ethical practice requires honest reporting of impairments, accurate maintenance records, suitable agent selection, and refusal to approve systems that do not match the hazard. A system should never be specified solely because it is inexpensive or familiar.

Contemporary practice increasingly uses electronic monitoring of valves, pumps, tank levels, alarms, and system impairments. Data analytics can identify recurring faults, but automated monitoring does not replace physical inspection. Artificial intelligence may assist with video smoke detection, maintenance prioritization, and risk analysis; however, false alarms, biased training data, cybersecurity, privacy, and accountability must be addressed. Life-safety decisions require validated systems and qualified human oversight.

Best-Practice Principles

• Identify the fuel, arrangement, ventilation, occupancy, and likely fire growth pattern.
• Select an agent compatible with the fuel and the consequences of discharge.
• Design for the actual hazard, not a generic occupancy label.
• Integrate detection, alarm, suppression, compartmentation, and evacuation.
• Provide adequate water, agent quantity, pressure, distribution, and enclosure integrity.
• Inspect, test, maintain, and document every critical component.
• Train personnel in recognition, alarm activation, extinguisher limitations, and evacuation.
• Treat extinguishment as incomplete until hidden heat and reignition risks are assessed.

Chapter Summary

Fire is a self-sustaining oxidation process requiring fuel, an oxidizer, heat, and chemical chain reactions. The fire tetrahedron explains why suppression can operate through cooling, oxygen exclusion, fuel removal, dilution, or chemical inhibition. Heat spreads by conduction, convection, radiation, and movement of fuel vapours, smoke, and embers.

Fire growth commonly progresses from incipient burning through growth, possible flashover, fully developed burning, and decay. Backdraft is a special hazard associated with oxygen-deficient compartments. Fire classes communicate the principal fuel involved, but real occupancies may contain several hazards.

Water, foam, carbon dioxide, clean agents, dry chemicals, and wet chemicals have different strengths and limitations. Fire load estimates the potential energy in combustibles and supports assessment of fire severity, but it does not by itself predict actual heat release. Effective fire safety combines suppression with detection, alarm, evacuation, passive protection, emergency planning, inspection, and maintenance.

Key Terms

Combustion: A chemical oxidation process that releases heat and often light.

Fuel: A substance capable of participating in combustion.

Oxidizer: A substance that supports oxidation, commonly atmospheric oxygen.

Pyrolysis: Thermal decomposition of a solid material producing combustible vapours.

Flash point: The lowest temperature at which a liquid produces sufficient vapour for ignition under specified conditions.

Fire triangle: Model consisting of fuel, heat, and oxygen.

Fire tetrahedron: Model adding chemical chain reaction to the fire triangle.

Conduction: Heat transfer through a material or direct contact.

Convection: Heat transfer by movement of a fluid such as air or smoke.

Radiation: Heat transfer by electromagnetic energy.

Flashover: Rapid transition to widespread involvement of combustible surfaces in a compartment.

Backdraft: Rapid combustion following introduction of air into a hot, oxygen-deficient compartment.

Cooling: Extinguishing action that removes heat from fuel or the flame zone.

Smothering: Excluding or reducing air contact with the fuel.

Starvation: Removing or isolating the fuel supply.

Chemical inhibition: Interruption of flame-propagating chemical reactions.

Fire load: Potential combustible energy present in a space or compartment.

Fire-load density: Fire load expressed per unit area.

Reignition: Return of combustion after apparent extinguishment.

Ventilation-limited fire: Fire whose burning rate is restricted primarily by available oxygen.

Review Questions

Short Answer Questions

1. What four elements are represented by the fire tetrahedron?
2. Distinguish conduction from convection.
3. Why can incomplete combustion produce carbon monoxide?
4. What is meant by cooling as an extinguishing mechanism?
5. Why can a fire reignite after visible flames disappear?

Long Answer Questions

1. Explain the stages of compartment-fire development and discuss the significance of flashover.
2. Compare water, foam, carbon dioxide, dry chemical, and wet chemical agents.
3. Explain how ventilation influences fire growth and suppression operations.
4. Describe the relationship between fire load, fire-load density, and potential fire severity.
5. Discuss why suppression systems must be integrated with detection, alarm, evacuation, and passive protection.

Analytical / Application Questions

1. A storage room contains ordinary combustibles, flammable liquids, and energized electrical equipment. Develop a preliminary suppression strategy and explain the limitations of relying on one agent for all hazards.
2. A closed room shows dense, pulsing smoke but little visible flame. Analyse the possible fire conditions and identify the safety issues that must be considered before opening the door.
3. A 200 m² room contains 1,000 kg of material with an effective heat of combustion of 18 MJ/kg. Calculate the potential fire energy and average fire-load density, then explain why these values do not predict the actual heat-release rate.

Multiple Choice Questions with Answers

Question 1

Which element was added to the traditional fire triangle to form the fire tetrahedron?

A. Smoke production

B. Chemical chain reaction

C. Fuel vapour pressure

D. Fire resistance

Correct Answer: B. Chemical chain reaction

Question 2

Which heat-transfer mechanism occurs through direct contact within a solid material?

A. Convection

B. Radiation

C. Conduction

D. Dilution

Correct Answer: C. Conduction

Question 3

Which extinguishing action primarily reduces the temperature of fuel below the level required for sustained combustion?

A. Cooling

B. Starvation

C. Chemical inhibition

D. Ventilation

Correct Answer: A. Cooling

Question 4

Which fire category commonly involves cooking oils and fats?

A. Class A

B. Class D

C. Class F or K

D. Electrical only

Correct Answer: C. Class F or K

Question 5

Why can water be particularly effective on many Class A fires?

A. It increases oxygen concentration

B. It absorbs substantial heat

C. It creates a flammable vapour

D. It chemically inhibits all flames

Correct Answer: B. It absorbs substantial heat

Question 6

What is a major hazard of carbon-dioxide total-flooding systems?

A. They increase room oxygen

B. They create deep water damage

C. They can produce an oxygen-deficient atmosphere

D. They are always electrically conductive

Correct Answer: C. They can produce an oxygen-deficient atmosphere

Question 7

Which condition is most associated with backdraft?

A. A fully ventilated outdoor spill

B. A hot, oxygen-deficient compartment receiving sudden air

C. A cooled room with no combustible material

D. A sprinkler discharge in an open courtyard

Correct Answer: B. A hot, oxygen-deficient compartment receiving sudden air

Question 8

A room contains 500 kg of material with an effective heat of combustion of 16 MJ/kg. What is its estimated potential fire energy?

A. 8 MJ

B. 32 MJ

C. 800 MJ

D. 8,000 MJ

Correct Answer: D. 8,000 MJ

Question 9

Which agent is specifically associated with forming a surface layer over hot cooking oils?

A. Wet chemical

B. Carbon dioxide only

C. Water jet

D. Metal powder

Correct Answer: A. Wet chemical

Question 10

Why may dry chemical suppression be followed by reignition?

A. It always adds fuel to the fire

B. It may provide limited cooling of deep-seated materials

C. It increases the fire load density

D. It prevents all heat transfer

Correct Answer: B. It may provide limited cooling of deep-seated materials