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Plant Process Safety > All about Fire and Explosions > Flashcards

All about Fire and Explosions Flashcards

1
Q

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

A

Flash Point

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2
Q

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

A

Auto-ignition point

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3
Q

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

A

Lower flammability limit

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4
Q

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

A

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

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5
Q

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

A

10% LEL

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6
Q

What is a Class A fire?

A

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

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7
Q

What is a Class B fire?

A

Fires involving flammable liquids

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8
Q

What is a Class C fire?

A

Fires involving electrical equipment

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9
Q

What is a Class D fire?

A

Fires involving combustible metals

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10
Q

What is a Class K fire?

A

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

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11
Q

Suggest 3 methods to prevent fires

A

Operate below the LFL/flash-point of liquid

Floating roof tanks

Use inert gas blanketing

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12
Q

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

A

oxygen

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13
Q

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

A

fuel

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14
Q

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

A

heat

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15
Q

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

A

White, uses foam

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16
Q

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

A

Red, uses water

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17
Q

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

A

Blue, dry powder

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18
Q

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

A

Black, carbon dioxide

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19
Q

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

A

Water (red) and foam (white) fire extinguishers

20
Q

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

A

True

21
Q

What is the definition of deflagration?

A

Sudden combustion in which flame velocity is less than sound velocity

22
Q

What is the definition of detonation?

A

Sudden combustion in which flame velocity is more than sound velocity

23
Q

What is the definition of an explosion?

A

Sudden & violent release of energy

24
Q

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

A

True.

25
Q

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

A
  1. Sudden release of flammable vapour gas upon vessel rupture
  2. Vapour disperses and mixes with air
  3. Ignition of vapour cloud, causing explosion
26
Q

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

A
  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.
27
Q

Describe how a dust explosion occurs.

A
  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
28
Q

What are the 9 methods of prevent explosions?

A
  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
29
Q

(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?

A

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.

30
Q

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

A
  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
31
Q

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

A
  1. Allows for free air circulation

2. Prevent collection of vapours in pockets and avoids collection of liquids

32
Q

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

A

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

33
Q

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

A
  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
34
Q

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?

A

True.

35
Q

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

A

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

36
Q

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

A

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

37
Q

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

A

Passive, under CPSS

38
Q

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

A

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

39
Q

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

A
  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.
40
Q

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

A

True

41
Q

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

A

True

42
Q

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

A

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

43
Q

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

A

During an explosion, local fires can develop.

44
Q

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

A

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

45
Q

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

A

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

46
Q

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?

A

True.

47
Q

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

A

Blue-coded, dry powder fire extinguishers

Plant Process Safety (3 decks)

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