7/29/2019 1.1 Introduction(1)
1/36
Techniques for AssessingIndustrial Hazards:
An Introduction
Dr. Samir I Abu-Eishah UAE University
1
7/29/2019 1.1 Introduction(1)
2/36
1- Techniques for Assessing Industrial
Hazards
1.1 Introduction
1.2 Definitions
1.3 Tasks of Hazard Assessment
1.4 Risk Reduction1.5 Computation of Risk
1.6 Acceptable and Maximum Risks
4- Consequence Calculations
4.1 Outflow Calculations
4.2 Behaviour Immediately after Release
4.3 Dispersion in the Atmosphere
4.4 Fires
4.5 Explosions4.6 Effects of Toxic Releases
2- The Structure of Hazard Analysis
2.1 Background
2.2 Description of the Hazard Analysis
Steps
5- Summary of Consequences
5.1 Results for Different Weather
Conditions
5.2 Ordering and Presenting The Results
3- Failure and Release Cases
3.1 Failure Cases
3.2 Release Cases
3.3 Properties of Released Materials
3.4 Consequences of a Release
6- Hazard Reduction
6.1 Reduction of Consequences
6.2 Reduction of Risk
6.3 Reduction of Impacts
2
Course Contents:
7/29/2019 1.1 Introduction(1)
3/36
1.1 Introduction
The chemical and energy industries use a wide variety of manufacturing,storage and control processes. These processes involve many different
types of material that can be potentially harmful if released into the
environment, because of their toxic, flammable or explosive properties.
These materials are not usually kept at atmospheric pressure and
temperature: modern chemical and energy industries involve highpressures and temperatures.
Gases are frequently liquefied by refrigeration to facilitate storage in bulk
quantities.
It is essential to achieve and maintain high standards of plant integritythrough good design, management and operational control.
3
7/29/2019 1.1 Introduction(1)
4/36
Introduction ...
Controls and safeguards developed by industry are supposed to beentirely effective.
Accidents do occur and can cause serious injury to employees or the
public, and damage to property. Therefore, it is essential to identify
potential hazards.
The necessary steps can then be taken to reduce the hazard (by design) or
the risk (by high operating standards, safety devices, etc.)
To conduct a hazard analysis it is important to follow a structured
approach.
In addition, the calculation methods used should be straightforward and
reliable.
4
7/29/2019 1.1 Introduction(1)
5/36
Introduction ...
In the initial stages of a hazard analysis it is appropriate toapply simplified techniques in order to identify the most
serious potential hazards. More sophisticated techniques can
then be used to assess methods of reducing the hazards.
The techniques for hazard analysis should be used inconjunction with other methods of safety assessment, as
appropriate for the plant being analyzed.
5
7/29/2019 1.1 Introduction(1)
6/36
Introduction ...
Some methods of hazard analysis are Hazard and Operability Studies (HAZOP),
Fault Tree Analysis,
Event Tree Analysis,
Failure Modes and Criticality Effect Analysis (FMECA).
The analyst might also use other methods of
identifying and ranking potential hazards, such as the
Dow Index or the ICI Mond Index.
6
7/29/2019 1.1 Introduction(1)
7/36
1.2 Definitions
Risk:
The probability of injury, disease or death underspecific circumstance (EPA)
The likelihood of a specified undesirable eventoccurring within a specified period or in specifiedcircumstances. (IChem E)
A measure of potential economic loss or humaninjury in terms ofthe probability of the loss orinjury occurring and the magnitude of the loss orinjury if it occurs. (AIChE)
7/29/2019 1.1 Introduction(1)
8/36
Definitions
Risk perception what people believe poses a risk or
hazard
Risk assessment quantifying the risk associatedwith a hazard
Risk management evaluating whether real or
perceived risks are acceptable, and if not, addressingthese risks.
7/29/2019 1.1 Introduction(1)
9/36
Definitions
Accident a specific unplanned event or sequence ofevents that has a specific undesirable consequence. Theelements of accidents are shown in Table 1.
Consequence the results of an accident event sequence.
Here, it is considered to be the fire, explosion, and releaseof toxic material that results from the accident, but not thehealth effects, economic loss, etc., which is the ultimateresult.
Health a state of complete physical, mental and social
well-being, not merely the absence of disease or infirmity(WHO)
Source: Battelle, Guidelines for Hazard Evaluation Procedures, AIChE, NewYork(1985).
9
7/29/2019 1.1 Introduction(1)
10/36
Hazard Initiating
Event/Upsets
Intermediate Events
(System or Operator Responses to Upsets)
Propagating Ameliorative
Accident
ConsequencesSignificant Inventories
of
a) Flammable
Materials
b) Combustible
Materials
c) Unstable Materials
d) Toxic Materials
e) Extremely Hot or
Cold Materials
f) Inerting Gases
(CH4, CO)
Machinery and
Equipment
Malfunctions
a) Pumps, Valves
b) Instruments,
Sensors
Process Parameter
Deviations
a) Pressure
b) Temperature
c) Flow Rate
d) Concentration
e) Phase/State Change
Safety System
Responses
a) Relief Valves
b) Back-up Utilities
c) Back-up
Components
d) Back-up Systems
Fires
Explosions
Impacts
Highly Reactive Containment Failures Containment Failures Mitigation System
Responses
a) Reagents
b) Products
c) Intermediate
Products
d) By-products
a) Pipes
b) Vessels
c) Storage Tanks
d) Gaskets
a) Pipes
b) Vessels
c) Storage Tanks
d) Gaskets, Bellows, etc.
e) Input/output or
venting
a) Vents
b) Dikes
c) Flares
d) Sprinklers
Dispersion of
Toxic Materials
Dispersion of
Highly Reactive
Materials
Table 1. Elements of Accidents
10
7/29/2019 1.1 Introduction(1)
11/36
11
Hazard Initiating Event/Upsets
Intermediate Events
(System or Operator Responses to Upsets)
Propagating Ameliorative
Accident
Consequences
Reaction Rates Especially
Sensitive toa) Impurities
b) Process Parameters
Human Errors
a) Operationsb) Maintenance
c) Testing
Material Releases
a) Combustiblesb) Explosive Materials
c) Toxic Materials
d) Reactive Materials
Control Responses
Operator Responsesa) Planned
b) Ad Hoc
Loss of Utilities
a) Electricity
b) Water
c) Aird) Steam
Ignition/Explosion
Operator Errors
a) Omission
b) Commissionc) Diagnosis/Decision
-Making
Contingency
Operations
a) Alarms
b) EmergencyProcedures
c) Personnel Safety
d) Evacuations
e) Security
External Events
a) Floods
b) Earthquakesc) Electrical Storms
d) High Winds
e) High Velocity Impacts
f) Vandalism
External Events
a) Delayed Warning
b) Unwarned
External Events
a) Early Detection
b) Early Warning
Method/Information
Errors
a) As Designed
b) As Communicated
Method/Information
Failure
a) Amount
b) Usefulness
c Timeliness
Information Flow
a) Routing
b) Methods
c) Timing
Table 1. Elements ofAccidents
7/29/2019 1.1 Introduction(1)
12/36
Definitions
Hazard:
The agent or means by which an adverse effect canoccur in a particular situation
A physical situation with a potential for human injury,damage to property, damage to environment or somecombination of these. (IChem E)
A characteristic of the system/plant/process thatrepresents a potential for an accident. (AIChE)
Typical Hazards are shown in Table 2.
12
7/29/2019 1.1 Introduction(1)
13/36
Table 2: Typical Hazards
Significant Inventories of: Extreme Physical Conditions: Flammable materials Combustible materials
Unstable materials
Corrosive materials
Asphyxiants
Shock sensitive materials
Highly reactive materials
Toxic materials
Inerting gases
Combustible dusts Pyrophoric materials
High temperatures Cryogenic temperatures
High pressures
Vacuum
Pressure cycling
Temperature cycling
Vibration/liquid
hammering
13
7/29/2019 1.1 Introduction(1)
14/36
Definitions
Hazard Identification:
The techniques for finding out what hazards are
present in a plant or process.
Hazard Assessment:
The techniques for deciding how far we ought to go
in removing the hazards or protecting people from
the hazards.
14
7/29/2019 1.1 Introduction(1)
15/36
Definitions
Incident the loss of containment of material or energy(e. g., a leak of 10 lb/sec of ammonia from a connectingpipeline to the ammonia tank, producing a toxic vaporcloud).
Incident Outcome - the physical manifestation of theincident;
for toxic materials: a toxic release (e. g., a 10 lb/sec leak of
ammonia).
for flammable materials: could be a BLEVE (Boiling Liquid
Expanding Vapor Explosion), flash fire, unconfined vapor
could explosion, etc.
15
7/29/2019 1.1 Introduction(1)
16/36
Definitions
Incident Outcome Case - the quantitative definition of a singleresult of an incident outcome through specification of sufficient
parameters to allow distinction of this case from all others for the
same incident outcome [e. g., a concentration of 3333 ppm (v) of
ammonia 2000 ft downwind from a 10 lb/sec ammonia leak is
estimated assuming a 1.4 mph wind, and Stability Class D].
Consequence a measure of the expected effects of an incident
outcome case [e. g., an ammonia cloud from a 10 lb/sec leak under
Stability Class D weather condition, and 1.4 mph wind traveling in a
northerly direction] will injure, say, 50 people.
Source: CCPS, Guidelines for Chemical Process Quantitative Risk Analysis,
AIChE, New York (1989)
16
7/29/2019 1.1 Introduction(1)
17/36
Relationship between Incidents, Incident Outcomes, and Incident
Outcome Cases for a hydrogen cyanide (HCN) release.
INCIDENTS INCIDENT OUTCOMES INCIDENT OUTCOME CASES
5 mph Wind, Stability Class A
Toxic Vapor 10 mph Wind, Stability Class D
Atmospheric Dispersion 15 mph Wind, Stability Class Eoooetc.
Jet Fire
Tank Full
BLEVE of Tank 50% Full
HCN Tank oooetc.
After 15 min. Release
Unconfined Vapor After 30 min. Release
Cloud Explosion After 60 min. Release
o
ooetc.
100 lb/minRelease ofHCN froma Tank Vent
17
7/29/2019 1.1 Introduction(1)
18/36
1.3 Tasks of Hazard Assessment
a) Identification and description of hazards (undesired events) that could
lead to undesirable consequences.
b) Identification of the mechanisms that could lead to the hazardous event,
i.e. accident event sequence.
c) A qualitative estimate of the likelihood and/or consequence of eachaccident event sequence, i.e. estimate the extent of any harmful effects.
d) A quantitative estimate of risk, which can be compared with acceptable
risk to determine whether or not expenditure on particular safety
measure is justified.
e) Judgments about the significance of the identified hazards and theestimated risks, i.e. making a relative ranking of the risk of each hazard
and accident event sequence.
f) Making and implementing decisions or courses of action, including ways
of reducing the likelihood or consequences of undesired events.
18
7/29/2019 1.1 Introduction(1)
19/36
hazard, risk, safety
+ analysis, assessment, evaluation
= ?
Hazard Identification = (a) + (b)
Hazard Analysis = (a) + (b) + (c) + (d)
qualitative
Risk Analysis = (a) + (b) + (c) + (d)
quantitative
(Hazard Assessment orEvaluation)= (a) + (b) + (c) + (d) + (e) + (f)
qualitative
Risk Assessment = (a) + (b) + (c) + (d) + (e) + (f)
quantitative 19
7/29/2019 1.1 Introduction(1)
20/36
Figure 1: The Risk Assessment Procedure
20
SystemDescription
HazardIdentification
AccidentProbabilitiesEstimation
RiskDetermination
RiskAcceptance ModifySystem
OperateSystem
AccidentConsequencesEstimation
No
Yes
7/29/2019 1.1 Introduction(1)
21/36
1.4 Risk Reduction
Possible Actions to Reduce Risk area change in the physical design and control system.
a change in the operating procedure.
a change in the process configuration or conditions.
a change in the process material.
a change in the testing, inspection/calibration and
maintenance procedure of the key safety items.
21
7/29/2019 1.1 Introduction(1)
22/36
Risk Reduction
The Risk Reduction Measures are classified to:
1. Substitution: those actions which eliminate the
hazard
2. Attenuation: those actions which reduce the
likelihood of its occurrence to an acceptable level.
3. Second Chance: those actions which eliminate or
reduce the hazard consequence.
22
7/29/2019 1.1 Introduction(1)
23/36
Risk Reduction
Example:Consider a reaction vessel where, in a HAZOP session, it wasdiscovered that if a certain impurity were introduced with one ofthe raw materials, there would be a sudden evolution of gas andan increase in pressure.
Solution: Eliminating the possibility of gas evolution by changing the raw
material responsible for the problem. (substitution)
Eliminating the possibility of gas evolution by altering one ofthe process conditions.(attenuation)
Fitting an appropriate pressure relief valve and vent system toprotect the plant.(second chance)
23
7/29/2019 1.1 Introduction(1)
24/36
1.5 Computation of Risk
The risk is simply computed by
R = P x S
R = risk,
P = probability (expressed as frequency, # of events/time),
S = severity (e.g., deaths, injuries, toxicity, etc.)
The term risk may be used qualitatively or quantitatively.
24
7/29/2019 1.1 Introduction(1)
25/36
Computation of Risk
In general form, the risk is computed by
fi = frequency of incident or rate at which the event occurs = (event / year)
xi = number of fatalities per event i = (deaths/event)
Ni = number of peoples exposed to event i= (number of exposed peoples per
event)
Pi = probability of fatalities among the exposed people = (deaths per exposed
people)
N = total number of peoples at risk
25
n
i
iii
n
i
ii fPNN
fxN
R11
11
7/29/2019 1.1 Introduction(1)
26/36
Fatal Accident Frequency Rate (FAFR)
26
)hours-exposed()employee(10
fatalitiesFAFR
8
(108 employee-exposed hour) is based on the total working hours of
(1000 employees) x (2000 exposed-hours/year) x (50 years/employee)
7/29/2019 1.1 Introduction(1)
27/36
1 worker year = 50 work weeks/year x 40 hours/weeks =
2000 hours
Based on cases per 100 worker years = 100 workers x 2000
hours/worker = 200,000 hours-worker exposure to hazard
Two types of calculation (1) based on injuries and illness (2)
based on lost workdays
OSHA (1) = number of injuries & illness x 200,000 / total
hours work by all employees during period covered
OSHA (2) = number of lost workdays x 200,000 / total hours
work by all employees during period covered
OSHA Incidence Rate
7/29/2019 1.1 Introduction(1)
28/36
Fatality Rate per Person (FRP)
and Annual Fatal Risk (AFR)
FRP = Annual deaths (work related) / (Total number of
employees)
= (deaths/year)/(number of employees)
AFR = (Rate of fatal accidents/hour) (Average annual
hours of work, hours/year)
= accidents/year
28
7/29/2019 1.1 Introduction(1)
29/36
Given FAR = 2. If employee works 8 hour per shift, 300 days per
year, compute the fatality rate.
Fatality rate = 8 h/day x 300 days/year x 2 deaths/108 h
= 4.8 x 10-5 death per person per year
More rock climbers are killed travelling by car than are killed
during rock climbing. Is this statement supported by statistics?
Solution: From data in next table, for travelling by car, FAR = 57,
for rock climbing, FAR = 4000. Rock climbing produces more fatalities per exposed hours but
spend more time(exposed hour) travelling by car. Think about
this.
Example
7/29/2019 1.1 Introduction(1)
30/36
Industry OSHA IncidenceRate
FAR(deaths/108hrs)
Chemical 0.49 4.0
Vehicle 1.08 1.3
Steel 1.54 8
Coal Mining 2.22 40
Construction 3.88 67
Agricultural 4.53 100
Activity FAR (deaths/108hrs) Fatality Rate
Travelling by car 57 17 x 10-5
Rock climbing 4000 4 x 10-5
OSHA and FAR
7/29/2019 1.1 Introduction(1)
31/36
1.6 Acceptable and Maximum Risks
Most treatment of acceptable risk deal primarily
with the risk of death. This may appear somewhat
arbitrary. But there is justification for this approach:
1. Data on fatalities are most possibly recorded and arerelatively straightforward.
2. (Number of fatalities) (Number of other injuries)
3. Measures which reduce death from a particular hazard
tend to reduce injuries as well.
31
7/29/2019 1.1 Introduction(1)
32/36
Risk Acceptability
7/29/2019 1.1 Introduction(1)
33/36
Acceptable Risk to Public
Voluntary: 10-5/person/year
Involuntarily:
Natural Disaster: 10-5/person/year
Man-made: 10-7/person/year
33
7/29/2019 1.1 Introduction(1)
34/36
Risk Acceptability
7/29/2019 1.1 Introduction(1)
35/36
Societal Risk Acceptability
7/29/2019 1.1 Introduction(1)
36/36
Maximum Risk to Public
The Maximum Risk to Public is averaged over the
whole population (Average Risk):
10-7/person/year
For anyone in public(Individual Risk):
10-5 to 10-6/person/year
36
Top Related