Fires and Explosion Flashcards
1
Q
Three most common chemical plant accidents
A
Fires, explosions and toxic releases
2
Q
The most common source of fires and explosions in the chemical industry
A
Organic solvents
3
Q
Engineers must be familiar with (3) to prevent accidents resulting from fires and explosions
A
- The fire and explosion properties of materials
- The nature of the fire and explosion process
- Procedures to reduce fire and explosion hazards
4
Q
Elements of Fire
A
Oxygen
Heat
Fuel
5
Q
Chemical Reaction between fuel, oxygen and heat
A
Fire
6
Q
Self-sustaining process of rapid oxidation or combustion of fuel
A
Fire
7
Q
Fire is the combustion of fuel, what is produced?
A
heat and light
8
Q
Major distinction between explosion and fire
A
rate of energy release
9
Q
Release of energy is slow
A
Fire
10
Q
Release energy is rapid, in order of microseconds
A
Explosion
11
Q
Fires can also result from explosion and explosion can result from fires (T/F)
A
T
12
Q
Is a chemical reaction in which a substance combines with an oxidant and releases energy
A
Combustion or Fire
13
Q
Part of the energy released in fire does what?
A
sustain the reaction
14
Q
May be caused by a flammable mixture coming in contact with a source of ignition with sufficient energy
A
Ignition
15
Q
A gas reaching a temperature high enough to cause the gas to autoignite
A
Ignition
16
Q
A fixed temperature above which adequate energy is available in the environment to provide an ignition source.
A
Autoignition Temperature (AIT)
17
Q
The temperature at which a product can undergo spontaneous ignition
A
AIT
18
Q
lowest Temperature of a liquid at which it gives off enough vapor to form an ignitable mixture with air
A
Flash Point
19
Q
Lowest temperature at which vapor above a liquid will continue to burn once ignited
A
Firepoint
20
Q
T/F: Flash point is higher than firepoint
A
F
21
Q
The range of concentration of gases in air
A
Flammability Limits
22
Q
Support the explosive process bounded by measurable limits called
A
UEL or UFL and LEL or LFL
23
Q
Gasoline vapors has LEL of
A
1.4%
24
Q
Gasoline vapors has UEL of
A
7.6%
25
A rapid expansion of gases resulting in a rapidly moving pressure or shock wave
Explosion
26
Expansion can be mechanical by means of?
Sudden rupture of pressurized vessel
27
Explosion resulting from sudden failure of a vessel containing high-pressure nonreactive gas
Mechanical
28
Explosion damage is caused by?
Pressure or shock wave
29
Pressure and shock wave can cause?
explosion damage
30
An explosion in which the reaction front moves at a speed less than the speed of sound in the unreacted medium
Deflagration
31
An explosion in which the reaction front moves at a speed greater than the speed of sound in the unreacted medium
Detonation
32
An explosion occurring within a vessel or a building
Confined explosion
33
THese are the most common and usually result in injury to the building inhabitants and extensive damage
Confined explosion
34
Occur in the open
Unconfined explosion
35
Result of a flammable gas spill
Unconfined explosion
36
The gas in this explosion is dispersed and mixed with air until it comes in contact with an ignition source
Unconfined explosion
37
Rarer to happen because the explosive material is frequently diluted below the LFL by wind dispersion
Unconfined explosion
38
Are destructive because large quantities of gas and large areas are frequently involved
Unconfined explosion
39
Occurs if the vessel that contains a liquid at a temperature above its atmospheric pressure boiling point ruptures
Boiling-Liquid Expanding-Vapor Explosion (BLEVE)
40
Subsequent BLEVE is what?
Explosive vaporization of a large fraction of the vessel contents
Possibly followed by combustion or
Explosion of the vaporized cloud (if it is combustible)
41
Occurs when an external fire heats the content within the tank of volatile material
BLEVE
42
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
vapor pressure, structural intergity
43
In BLEVE, when the tank ruptures, the hot liquid?
Volatilizes explosively
44
Results from rapid combustion of fine solid particles
Dust explosion
45
Many solid materials (common metals such as iron and aluminum) become flammable when reduced to fine powder (T/F)
T
46
Abrupt pressure wave moving though a gas
Shock wave
47
This is followed by a strong wind
Shock wave in open air
48
The pressure increase in the shock wave is ____ that the process is mostly _____
rapid, adiabatic
49
Is expected from highly explosive materials such as TNT but can also occur from sudden rupture of a pressure vessel
Shock wave
50
Combined shock wave and strong wind
Blast wave
51
Pressure wave propagating in air
Blast wave
52
Pressure on an object as a result of an impacting shock wave
Overpressure
53
Minimum energy input required ti initiate combustion
Minimum ignition energy
54
All flammable materials (including dust) have MIEs (T/F)
T
55
Where doe MIE depends (4)
Specific chemical or mixture
concentration
pressure
temperature
56
Explosions that occur because of the release of the flammable vapor over large volume
Vapor cloud explosion (VCE)
57
Are most commonly deflagrations
VCS
58
Simple method for equating a known energy of a combustible fuel to an equivalent mass of TNT
TNT equivalency
59
Based on assumption that an exploding fuel mass behaves like exploding TNT on an equivalent energy basis
TNT equivalency
60
Typical values for energy of explosion of TNT (cal/g)
1120
61
Typical values for energy of explosion of TNT (kJ/kg)
4686
62
Typical values for energy of explosion of TNT (btu/lb)
2016
63
This can be used in place of the energy of explosion for the combustible gas
heat of combustion for the flammable gas
64
Results from a chemical explosion generated by the expansion of gases at the explosion site
Blast wave
65
Expansion can be caused by two mechanisms:
1. thermal heating of the reaction products
2. the change in the total number of moles by reaction
66
Energy released during a reaction explosion is computed using?
Standard thermodynamics
67
T/F: The released energy is equal to the work required to expand the gases
T
68
Expansion work is a form of mechanical energy (T/F)
T
69
An explosion occurring in a confined vessel or structure can rupture the vessel resulting in the projection of debris over a wide area.
Missile damage
70
Can cause appreciable injury to people and damage to structures and process equipment
Debris or Missiles
71
Also create missiles by blast wave impact and subsequent translation of structures
Unconfined ecplosions
72
A means by which an accident propagates throughout the plant
Missiles
73
When debris strikes storage tanks and other process equipment, what is the result?
Secondary fires or explosions
74
People can be injured by explosions from ?
Direct blast effects
75
Types of direct blast effects
overpressure nad thermal radiation
76
These are estimated using probit
Blast damage effects
77
Blast damage effects can be estimated using
probit / probability unit
78
The most dangerous and destructive explosions in the chemical process industries
Vapor Cloud explosions
79
Sequence of steps in the occurrence of VC Explosions
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
Special type of accident that can release large quantities of materials
BLEVE
81
If the material is flammable, what might result?
VCE
82
Occurs when a tank containing a liquid held above its atmospheric pressure boiling point ruptures
BLEVE
83
The most common type of BLEVE is caused by ?
Fire
84
BLEVE occurrence steps
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
If the liquid is flammable and a fire is the cause of the BLEVE, the liquid may?
ignite as the tank ruptures
86
Often, the boiling liquid behaves as a ____ propelling vessel parts for great distances
rocket
87
If the BLEVE is not caused by fire, what might form?
Vapor cloud resulting in a VCE
88
The vapors also might be hazardous to personnel by means of ?
skin burns or toxic effects
89
When BLEVE occurs in a vessel, only a fraction of the _____ vaporizes
liquid
90
The amount of liquid that vaporizes when BLEVE occurs in a vessel depends on ?
physical and thermodynamic conditions of the vessel content
91
Twofold strategy used to limit the potential damage from fires and explosions
Prevent the initiation of the fire or explosion
Minimize the damage after a fire or explosion has occurred
92
Common method of F nad E prevention
Use of Flammability diagram
Sprinkler systems
Explosion-proof equipment and instruments
Ventilation
Controlling static electricity
Inerting
93
Process of adding an inert gas to a combustible mixture to reduce the concentration of oxygen below the limiting oxygen concentration (LOC)
Inerting
94
The inert gas is usually?
Nitrogen, CO2 or steam
95
For many gases the LOC is ?
10%
96
For many dusts the LOC is?
8%
97
Where does inerting begins?
1. Initial purge of the vessel with inert gas to bring oxygen to safe concentrations
2. Flammable material is charged
98
What is required to maintain an inert atmosphere in the vapor space above the liquid?
Inerting system
99
Charge buildup results
sparks
100
is an inevitable event if control methods are not appropriately used
ignition of flammable materials
101
Engineers recognize the problem and install special features to prevent (2)
1. sparks by eliminating the buildup and accumulation of static charge
2. inerting the surrounding
102
Most effective and reliable method for preventing ignition is?
Interting
103
This is always used when working with flammable liquids that are 5°C (or less) below the flash point (closed cup)
Inerting
104
Design objective for controlling static electricity is
1. Prevent the buildup of charges on a product as well as the surrounding objects
105
Foe every charged object there exists its _____ counterpart
oppositely charged
106
Three methods for achieving the design objective:
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
Measures to mitigate the consequences of an explosion
deflagration venting
explosion suppression
108
Streaming current Is is produces during the _____ when pumping fluids into a vessel through a pipe on top
separation process
109
Basis of charge buildup
Streaming current
110
Adding an enlarged section of pipe just before entering the tank, providing time for charge reduction
Relaxation
111
Voltage difference between two conductive materials is reduced to zero during?
Bonding two conductive materials
112
If sets of the bonded materials have different voltages, it can be set to zero through
Grounding
113
Ground level or
Zero voltage
114
Eliminates the charge buildup between various parts of system, eliminating the potential for static sparks
Bonding and Grounding
115
An extended line that reduces the electrical charge that accumulates when liquid is allowed to free fall
Dip leg or Dip pipe
116
When using dip leg care is a must to avoid?
Siphoning back when the inlet is stopped
117
Common method used in dip piping is?
place a hole in the dip pipe near the top of the vessel
118
Another method for dip piping is?
Use angle iron instead of pipe and let the liquid flow down
119
These methods are also used in filling drums
Hole and angle iron
120
Another method to prevent fires and explosions to dilute the explosive vapors with air and confine the hazardous flammable mixtures
Proper Ventilation
121
Are recommended because the average wind velocity are high enough to safely dilute volatile chemical leaks that may exist within the plant
Open-Air Plants
122
If processes cannot be constructed outside, local and dilution ventilation are required
Plants inside the building
123
Most effective method for controlling flammable gas releases
Local ventilation
124
When the potential points of releases are numerous, what is used?
Dilution ventilation
125
T/F: All electrical devices are inherent ignition sources
T
126
T/F: The fire and explosion hazards is directly proportional to the number and type of electrically powered devices in the process area
T
127
Process areas are divided into two major types of environment:
XP or Explosion proof
Non-XP
128
Means flammable materials (vapors) might be present at certain times
XP
129
Means that flammable materials are not present, even abnormal conditions
Non-Xp
130
Designated open flames, heated elements and other sources of ignition may be present
Non-xp
131
Are effective way to contain fires
Sprinkler Systems
132
Consists of an array of sprinkler heads connected to water supply
Sprinkler systems
133
Are mounted in a high location usually near ceilings and disperse a fine spray of water over an area when activated
heads
134
2 Methods of Activating Sprinkler Systems
1. Wet-pipe system
2. Deluge System
135
Activates the head individually melting the fusible link holding a plug in the head assembly
Wet-pipe system
136
Once activated, the system cannot be turned off unless the main water supply is stopped
Wet-pipe system
137
Used for storage area, laboratories, control rooms and small pilot areas
Wet pipe systems
138
Activates the entire sprinkler array from a common control point
Deluge system
139
The control point is connected to an array of ___ and _____ detectors that start the sprinklers when an abnormal condition is detected
heat, smoke
140
Used for plant process areas and larger pilot plants
Deluge systems
141
