All about Fire and Explosions

Question 1

The lowest temperature at which a substance gives off enough vapour to form a flammable mixture with air is known as the ______

Answer 1

Flash Point

Question 2

The lowest temperature at which a substance will ignite spontaneously is known as the _______

Answer 2

Auto-ignition point

Question 3

The lowest concentration at which a combustible gas in air can burn is known as the ______

Answer 3

Lower flammability limit

Question 4

The lower flammability limit (LFL) is not always equivalent to the lower explosive limit (LEL). True or false?

Answer 4

False. LFL = LEL, both can be used interchangeably.

Question 5

What is a suitable alarm limit to be used to trigger alerts to plant operators on the presence of flammable gases in the air?

Answer 5

10% LEL

Question 6

What is a Class A fire?

Answer 6

Fires of common items like wood, paper, cloth, rubber and plastics

Question 7

What is a Class B fire?

Answer 7

Fires involving flammable liquids

Question 8

What is a Class C fire?

Answer 8

Fires involving electrical equipment

Question 9

What is a Class D fire?

Answer 9

Fires involving combustible metals

Question 10

What is a Class K fire?

Answer 10

Fires involving cooking media, such as oils and grease found in kitchens

Question 11

Suggest 3 methods to prevent fires

Answer 11

Operate below the LFL/flash-point of liquid

Floating roof tanks

Use inert gas blanketing

Question 12

In the context of the fire triangle, smothering a flame refers to removing _____

Answer 12

oxygen

Question 13

In the context of the fire triangle, starving a flame refers to removing _____

Answer 13

fuel

Question 14

In the context of the fire triangle, cooling a flame refers to removing _____

Answer 14

heat

Question 15

A fire extinguisher used for petrol fires is color coded ____ and uses _____

Answer 15

White, uses foam

Question 16

A fire extinguisher used for cloth and paper fires is color coded ____ and uses _____

Answer 16

Red, uses water

Question 17

A fire extinguisher used for electrical fires is color coded ____ and uses _____

Answer 17

Blue, dry powder

Question 18

A fire extinguisher used for electrical fires is color coded ____ and uses _____

Answer 18

Black, carbon dioxide

Question 19

What types of fire extinguishers cannot be used for electrical fires?

Answer 19

Water (red) and foam (white) fire extinguishers

Question 20

Concrete is a suitable material for fire-proofing. True or false?

Answer 20

True

Question 21

What is the definition of deflagration?

Answer 21

Sudden combustion in which flame velocity is less than sound velocity

Question 22

What is the definition of detonation?

Answer 22

Sudden combustion in which flame velocity is more than sound velocity

Question 23

What is the definition of an explosion?

Answer 23

Sudden & violent release of energy

Question 24

Detonations are many times louder than deflagrations. True or false?

Answer 24

True.

Question 25

Describe the steps leading to a vapour cloud explosion (VCE)

Answer 25

1. Sudden release of flammable vapour gas upon vessel rupture 2. Vapour disperses and mixes with air 3. Ignition of vapour cloud, causing explosion

Question 26

Describe the steps leading to a boiling liquid expanding vapor explosion (BLEVE)

Answer 26

1. Vessel contains liquid under pressure is exposed to fire. Liquid heats up, vapour pressure rises. 2. At set P of relief valve, vapour is released, and liquid level falls. 3. Proportion of vessel wall which has benefit of liquid cooling reduces. 4. As flame continues to impinge on unwetted vessel surface, vessel wall may weaken and fail 5. Vessel suddenly ruptures, propelling dangerous shrapnel over long distances. Superheated liquid expands rapidly. 6. If ensuring vapours are flammable, ignition may follow, and a huge fireball is formed with high pressure effects.

Question 27

Describe how a dust explosion occurs.

Answer 27

1. They occur when a cloud of finely dispersed particles of combustible dust is ignited 2. Dust explosions occur in the presence of fuel (combustible dust), oxygen, a source of ignition and dispersion of dust within a confined space 3. There is normally a primary explosion, followed by a more violent secondary explosion, followed by an even more violent tertiary explosion

Question 28

What are the 9 methods of prevent explosions?

Answer 28

1. Dilution ventilation; Supply air to dilute flammable mixture 2. Exhaust ventilation; Remove build-up of flammable dust within a space. 3. Avoid congestion; Minimum spacing between equipment. 4. Avoid release of combustible vapours to atmosphere; Relief systems and closed-loop sampling techniques. 5. Employ gas detection systems. 6. Employ inert gas blanketing to minimise O2 concentration 7. Location of buildings 8. Water spray systems 9. Fireproofing

Question 29

(Ventilation) In designing a candy-making factory, the technical manager suggested placing the process equipment in an indoor area. Why is this not a good idea?

Answer 29

Enclosed locations do not have adequate ventilation, and may allow the build-up of combustible, dispersed candy dust in a confined area. If a source of ignition is present, a dust explosion could result.

Question 30

(Ventilation) Why is it not recommended to install walls and roofs in a factory handling combustible materials?

Answer 30

1. They tend to block vision and access 2. They reduce ventilation, allowing combustible vapours and dust to accumulate 3. They may collapse and cause damage to plant or personnel in the event of an explosion or deflagration

Question 31

(Ventilation) In terms of reducing the risk of explosions and increased explosion protection, open grating is preferred because it

Answer 31

1. Allows for free air circulation | 2. Prevent collection of vapours in pockets and avoids collection of liquids

Question 32

(Ventilation) In what scenario is solid floors preferred to open grating?

Answer 32

There is a need to offer a fire and gas barrier or spill protection

Question 33

Suggest 3 methods to avoid the release of combustible gases or vapours into the atmosphere

Answer 33

1. Waste combustible vapours should be routed to flare or returned to process through a closed header 2. Sampling techniques should use a closed system 3. Use a sealed drainage system for process equipment 4. Avoid open drain ports and provide a separate sewage and oily water drain system

Question 34

Equipment that handle large amounts of highly volatile equipment should be positioned so that the prevailing wind direction will disperse potential releases to locations that would not endanger other equipment or provide an ignition source. Is this true or false?

Answer 34

True.

Question 35

Fireproofing is done in all areas in a chemical plant. Is this true or false?

Answer 35

False. Fireproofing is usually installed at locations where fire risk exposures are considered prevalent, such as pumps and compressors.

Question 36

Steel should be used because it does not lose its strength, even when exposed to a hydrocarbon fire. Is this true or false?

Answer 36

False. Ordinary steel has been shown to lose its strength rapidly at temperature increases above 260C. At 540C, its strength is cut in half.

Question 37

Installing fire-resistant walls in a chemical plant that handles combustible vapours is considered what kind of safety strategy?

Answer 37

Passive, under CPSS

Question 38

The ideal fire protection measure is one that is actively monitoring the process for risk of fire. Is this true or false?

Answer 38

False. The ideal fire protection is one that does not require additional action to implement, and is always in place.

Question 39

What are the 3 types of events that can cause damage in an explosion?

Answer 39

1. Overpressure; The pressure between the explosion's expanding gas and its surrounding atmosphere. 2. Pulse. The differential pressure across a plant as a pressure wave passes. 3. Missiles and shrapnel; Items thrown by the blast of expanding gases.

Question 40

Detonations have a greater shattering effect than deflagrations. True or false?

Answer 40

True

Question 41

Detonations tend to occur in vessels, pipes and other confined spaces as shock waves are difficult to disperse. True or false?

Answer 41

True

Question 42

How do water sprays help to prevent the risk of explosions?

Answer 42

They assist in diluting the vapours or gases with the induced air current created by the velocity of the projected water particles. `

Question 43

Why is fireproofing an important part of mitigating the damage from explosions?

Answer 43

During an explosion, local fires can develop.

Question 44

What is the most critical event that could cause damage in an explosion?

Answer 44

Overpressure, from the pressure between the explosion expanding gas and the surrounding atmosphere..

Question 45

Explain why a water spray fire extinguisher is not effective for Class B (liquid) fires.

Answer 45

Water spray is not effective for extinguishing fires caused by immiscible liquids.

Question 46

Except for water & vaporising liquids, foam, dry powder and carbon dioxide serve to extinguish a fire by smothering the flame. Is this true or false?

Answer 46

True.

Question 47

What is a suitable fire extinguisher to extinguish fires caused by combustible metals?

Answer 47

Blue-coded, dry powder fire extinguishers