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PROCESS SAFETY > Fires and Explosion > Flashcards

Fires and Explosion Flashcards

1
Q

Three most common chemical plant accidents

A

Fires, explosions and toxic releases

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2
Q

The most common source of fires and explosions in the chemical industry

A

Organic solvents

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3
Q

Engineers must be familiar with (3) to prevent accidents resulting from fires and explosions

A
  1. The fire and explosion properties of materials
  2. The nature of the fire and explosion process
  3. Procedures to reduce fire and explosion hazards
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4
Q

Elements of Fire

A

Oxygen
Heat
Fuel

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5
Q

Chemical Reaction between fuel, oxygen and heat

A

Fire

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6
Q

Self-sustaining process of rapid oxidation or combustion of fuel

A

Fire

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7
Q

Fire is the combustion of fuel, what is produced?

A

heat and light

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8
Q

Major distinction between explosion and fire

A

rate of energy release

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9
Q

Release of energy is slow

A

Fire

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10
Q

Release energy is rapid, in order of microseconds

A

Explosion

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11
Q

Fires can also result from explosion and explosion can result from fires (T/F)

A

T

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12
Q

Is a chemical reaction in which a substance combines with an oxidant and releases energy

A

Combustion or Fire

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13
Q

Part of the energy released in fire does what?

A

sustain the reaction

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14
Q

May be caused by a flammable mixture coming in contact with a source of ignition with sufficient energy

A

Ignition

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15
Q

A gas reaching a temperature high enough to cause the gas to autoignite

A

Ignition

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16
Q

A fixed temperature above which adequate energy is available in the environment to provide an ignition source.

A

Autoignition Temperature (AIT)

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17
Q

The temperature at which a product can undergo spontaneous ignition

A

AIT

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18
Q

lowest Temperature of a liquid at which it gives off enough vapor to form an ignitable mixture with air

A

Flash Point

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19
Q

Lowest temperature at which vapor above a liquid will continue to burn once ignited

A

Firepoint

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20
Q

T/F: Flash point is higher than firepoint

A

F

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21
Q

The range of concentration of gases in air

A

Flammability Limits

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22
Q

Support the explosive process bounded by measurable limits called

A

UEL or UFL and LEL or LFL

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23
Q

Gasoline vapors has LEL of

A

1.4%

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24
Q

Gasoline vapors has UEL of

A

7.6%

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25
Q

A rapid expansion of gases resulting in a rapidly moving pressure or shock wave

A

Explosion

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26
Q

Expansion can be mechanical by means of?

A

Sudden rupture of pressurized vessel

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27
Q

Explosion resulting from sudden failure of a vessel containing high-pressure nonreactive gas

A

Mechanical

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28
Q

Explosion damage is caused by?

A

Pressure or shock wave

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29
Q

Pressure and shock wave can cause?

A

explosion damage

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30
Q

An explosion in which the reaction front moves at a speed less than the speed of sound in the unreacted medium

A

Deflagration

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31
Q

An explosion in which the reaction front moves at a speed greater than the speed of sound in the unreacted medium

A

Detonation

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32
Q

An explosion occurring within a vessel or a building

A

Confined explosion

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33
Q

THese are the most common and usually result in injury to the building inhabitants and extensive damage

A

Confined explosion

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34
Q

Occur in the open

A

Unconfined explosion

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35
Q

Result of a flammable gas spill

A

Unconfined explosion

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36
Q

The gas in this explosion is dispersed and mixed with air until it comes in contact with an ignition source

A

Unconfined explosion

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37
Q

Rarer to happen because the explosive material is frequently diluted below the LFL by wind dispersion

A

Unconfined explosion

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38
Q

Are destructive because large quantities of gas and large areas are frequently involved

A

Unconfined explosion

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39
Q

Occurs if the vessel that contains a liquid at a temperature above its atmospheric pressure boiling point ruptures

A

Boiling-Liquid Expanding-Vapor Explosion (BLEVE)

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40
Q

Subsequent BLEVE is what?

A

Explosive vaporization of a large fraction of the vessel contents
Possibly followed by combustion or
Explosion of the vaporized cloud (if it is combustible)

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41
Q

Occurs when an external fire heats the content within the tank of volatile material

A

BLEVE

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42
Q

During BLEVE, as the tank contents heat, the ____ of the liquid within the tank increases and the tank’s ______ is reduced because of the heating

A

vapor pressure, structural intergity

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43
Q

In BLEVE, when the tank ruptures, the hot liquid?

A

Volatilizes explosively

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44
Q

Results from rapid combustion of fine solid particles

A

Dust explosion

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45
Q

Many solid materials (common metals such as iron and aluminum) become flammable when reduced to fine powder (T/F)

A

T

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46
Q

Abrupt pressure wave moving though a gas

A

Shock wave

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47
Q

This is followed by a strong wind

A

Shock wave in open air

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48
Q

The pressure increase in the shock wave is ____ that the process is mostly _____

A

rapid, adiabatic

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49
Q

Is expected from highly explosive materials such as TNT but can also occur from sudden rupture of a pressure vessel

A

Shock wave

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50
Q

Combined shock wave and strong wind

A

Blast wave

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51
Q

Pressure wave propagating in air

A

Blast wave

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52
Q

Pressure on an object as a result of an impacting shock wave

A

Overpressure

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53
Q

Minimum energy input required ti initiate combustion

A

Minimum ignition energy

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54
Q

All flammable materials (including dust) have MIEs (T/F)

A

T

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55
Q

Where doe MIE depends (4)

A

Specific chemical or mixture
concentration
pressure
temperature

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56
Q

Explosions that occur because of the release of the flammable vapor over large volume

A

Vapor cloud explosion (VCE)

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57
Q

Are most commonly deflagrations

A

VCS

58
Q

Simple method for equating a known energy of a combustible fuel to an equivalent mass of TNT

A

TNT equivalency

59
Q

Based on assumption that an exploding fuel mass behaves like exploding TNT on an equivalent energy basis

A

TNT equivalency

60
Q

Typical values for energy of explosion of TNT (cal/g)

A

1120

61
Q

Typical values for energy of explosion of TNT (kJ/kg)

A

4686

62
Q

Typical values for energy of explosion of TNT (btu/lb)

A

2016

63
Q

This can be used in place of the energy of explosion for the combustible gas

A

heat of combustion for the flammable gas

64
Q

Results from a chemical explosion generated by the expansion of gases at the explosion site

A

Blast wave

65
Q

Expansion can be caused by two mechanisms:

A
  1. thermal heating of the reaction products
  2. the change in the total number of moles by reaction
66
Q

Energy released during a reaction explosion is computed using?

A

Standard thermodynamics

67
Q

T/F: The released energy is equal to the work required to expand the gases

A

T

68
Q

Expansion work is a form of mechanical energy (T/F)

A

T

69
Q

An explosion occurring in a confined vessel or structure can rupture the vessel resulting in the projection of debris over a wide area.

A

Missile damage

70
Q

Can cause appreciable injury to people and damage to structures and process equipment

A

Debris or Missiles

71
Q

Also create missiles by blast wave impact and subsequent translation of structures

A

Unconfined ecplosions

72
Q

A means by which an accident propagates throughout the plant

A

Missiles

73
Q

When debris strikes storage tanks and other process equipment, what is the result?

A

Secondary fires or explosions

74
Q

People can be injured by explosions from ?

A

Direct blast effects

75
Q

Types of direct blast effects

A

overpressure nad thermal radiation

76
Q

These are estimated using probit

A

Blast damage effects

77
Q

Blast damage effects can be estimated using

A

probit / probability unit

78
Q

The most dangerous and destructive explosions in the chemical process industries

A

Vapor Cloud explosions

79
Q

Sequence of steps in the occurrence of VC Explosions

A
  1. Sudden release of a large quantity of flammable vapor (superheated and pressurized liquid)
  2. Dispersion of the vapor throughout the plant site while mixing with air
  3. Ignition of the resulting vapor cloud
80
Q

Special type of accident that can release large quantities of materials

A

BLEVE

81
Q

If the material is flammable, what might result?

A

VCE

82
Q

Occurs when a tank containing a liquid held above its atmospheric pressure boiling point ruptures

A

BLEVE

83
Q

The most common type of BLEVE is caused by ?

A

Fire

84
Q

BLEVE occurrence steps

A
  1. Fire develops adjacent to a tank containing a liquid
  2. Fire heats the walls of the tank
  3. The tank walls below liquid level are cooled by the liquid, increasing the liquid temperature and pressure in the tank
  4. the flames reach the tank wall or roof where there is only a vapor and no liquid to remove the heat, the tank metal temperature rises until the tank loses its structural strength
  5. The tank ruptures, explosively vaporizing the contents
85
Q

If the liquid is flammable and a fire is the cause of the BLEVE, the liquid may?

A

ignite as the tank ruptures

86
Q

Often, the boiling liquid behaves as a ____ propelling vessel parts for great distances

A

rocket

87
Q

If the BLEVE is not caused by fire, what might form?

A

Vapor cloud resulting in a VCE

88
Q

The vapors also might be hazardous to personnel by means of ?

A

skin burns or toxic effects

89
Q

When BLEVE occurs in a vessel, only a fraction of the _____ vaporizes

A

liquid

90
Q

The amount of liquid that vaporizes when BLEVE occurs in a vessel depends on ?

A

physical and thermodynamic conditions of the vessel content

91
Q

Twofold strategy used to limit the potential damage from fires and explosions

A

Prevent the initiation of the fire or explosion
Minimize the damage after a fire or explosion has occurred

92
Q

Common method of F nad E prevention

A

Use of Flammability diagram
Sprinkler systems
Explosion-proof equipment and instruments
Ventilation
Controlling static electricity
Inerting

93
Q

Process of adding an inert gas to a combustible mixture to reduce the concentration of oxygen below the limiting oxygen concentration (LOC)

A

Inerting

94
Q

The inert gas is usually?

A

Nitrogen, CO2 or steam

95
Q

For many gases the LOC is ?

A

10%

96
Q

For many dusts the LOC is?

A

8%

97
Q

Where does inerting begins?

A
  1. Initial purge of the vessel with inert gas to bring oxygen to safe concentrations
  2. Flammable material is charged
98
Q

What is required to maintain an inert atmosphere in the vapor space above the liquid?

A

Inerting system

99
Q

Charge buildup results

A

sparks

100
Q

is an inevitable event if control methods are not appropriately used

A

ignition of flammable materials

101
Q

Engineers recognize the problem and install special features to prevent (2)

A
  1. sparks by eliminating the buildup and accumulation of static charge
  2. inerting the surrounding
102
Q

Most effective and reliable method for preventing ignition is?

A

Interting

103
Q

This is always used when working with flammable liquids that are 5°C (or less) below the flash point (closed cup)

A

Inerting

104
Q

Design objective for controlling static electricity is

A
  1. Prevent the buildup of charges on a product as well as the surrounding objects
105
Q

Foe every charged object there exists its _____ counterpart

A

oppositely charged

106
Q

Three methods for achieving the design objective:

A
  1. Reducing the rate of charge generation and increase rate of relaxation (liquids)
  2. Designing the system to include charge reduction by means of low-energy discharge (powders)
  3. Maintain oxidant levels below the combustible levels (inerting)
    Maintain fuel levels below LFL or above UFL
107
Q

Measures to mitigate the consequences of an explosion

A

deflagration venting
explosion suppression

108
Q

Streaming current Is is produces during the _____ when pumping fluids into a vessel through a pipe on top

A

separation process

109
Q

Basis of charge buildup

A

Streaming current

110
Q

Adding an enlarged section of pipe just before entering the tank, providing time for charge reduction

A

Relaxation

111
Q

Voltage difference between two conductive materials is reduced to zero during?

A

Bonding two conductive materials

112
Q

If sets of the bonded materials have different voltages, it can be set to zero through

A

Grounding

113
Q

Ground level or

A

Zero voltage

114
Q

Eliminates the charge buildup between various parts of system, eliminating the potential for static sparks

A

Bonding and Grounding

115
Q

An extended line that reduces the electrical charge that accumulates when liquid is allowed to free fall

A

Dip leg or Dip pipe

116
Q

When using dip leg care is a must to avoid?

A

Siphoning back when the inlet is stopped

117
Q

Common method used in dip piping is?

A

place a hole in the dip pipe near the top of the vessel

118
Q

Another method for dip piping is?

A

Use angle iron instead of pipe and let the liquid flow down

119
Q

These methods are also used in filling drums

A

Hole and angle iron

120
Q

Another method to prevent fires and explosions to dilute the explosive vapors with air and confine the hazardous flammable mixtures

A

Proper Ventilation

121
Q

Are recommended because the average wind velocity are high enough to safely dilute volatile chemical leaks that may exist within the plant

A

Open-Air Plants

122
Q

If processes cannot be constructed outside, local and dilution ventilation are required

A

Plants inside the building

123
Q

Most effective method for controlling flammable gas releases

A

Local ventilation

124
Q

When the potential points of releases are numerous, what is used?

A

Dilution ventilation

125
Q

T/F: All electrical devices are inherent ignition sources

A

T

126
Q

T/F: The fire and explosion hazards is directly proportional to the number and type of electrically powered devices in the process area

A

T

127
Q

Process areas are divided into two major types of environment:

A

XP or Explosion proof
Non-XP

128
Q

Means flammable materials (vapors) might be present at certain times

A

XP

129
Q

Means that flammable materials are not present, even abnormal conditions

A

Non-Xp

130
Q

Designated open flames, heated elements and other sources of ignition may be present

A

Non-xp

131
Q

Are effective way to contain fires

A

Sprinkler Systems

132
Q

Consists of an array of sprinkler heads connected to water supply

A

Sprinkler systems

133
Q

Are mounted in a high location usually near ceilings and disperse a fine spray of water over an area when activated

A

heads

134
Q

2 Methods of Activating Sprinkler Systems

A
  1. Wet-pipe system
  2. Deluge System
135
Q

Activates the head individually melting the fusible link holding a plug in the head assembly

A

Wet-pipe system

136
Q

Once activated, the system cannot be turned off unless the main water supply is stopped

A

Wet-pipe system

137
Q

Used for storage area, laboratories, control rooms and small pilot areas

A

Wet pipe systems

138
Q

Activates the entire sprinkler array from a common control point

A

Deluge system

139
Q

The control point is connected to an array of ___ and _____ detectors that start the sprinklers when an abnormal condition is detected

A

heat, smoke

140
Q

Used for plant process areas and larger pilot plants

A

Deluge systems

141
Q
A

PROCESS SAFETY (3 decks)

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