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Hazard and Risk Analysis
Tools
[American stuntmen are smart - they think about safety. When they do a jump in a car, they calculate everything: the speed, the distance...
But in Hong Kong, we don't know how to count. Everything we do is a guess. If you've got the guts, you do it. All of my stuntmen have gotten
hurt. ] Jackie Chan.
Overview of Risk Assessment
Hazard A potentially harmful source or situation in which may cause
injury, fatality or health effects to user , property damages or environmental damages; or any combinations of the effects
Risk A combination of the likelihood of an occurrence of a hazardous
event with specified period or in specified circumstances and the severity of injury or damage to the health of people, property, environment or any combination of these caused by the event
Risk = Probability of Hazard Occurrence X
Severity of Hazard
Who will carry out
risk assessment??
• By: • Person or persons trained to
identify hazard and risk assessment
• Legally competent person • E.g. : CIMAH assessor,
Chemical Health Risk Assessor
• With • Consultation with an
involvement of workers • Safety and health
committee • Area representatives • Supervisors
Safety Analysis
1.Hazard Identification, Risk Assessment and Risk Control (HIRARC)
2.Fault Tree Analysis
3.Event Tree Analysis
1 Hazard Identification, Risk
Assessment and Risk Control (HIRARC)
HIRARC
One of the general duties as prescribed under the Occupational Safety and Health Act 1994 (Act 514) for the employer.
The specific purpose of HIRARC are as follows:-
a. to identify all the factors that may cause harm to employees and others (the hazards);
b. to consider what the chances are of that harm actually be falling anyone in the circumstances of a particular case and the possible severity that could come from it (the risks); and
c. to enable employers to plan, introduce and monitor preventive measures to ensure that the risks are adequately controlled at all times.
HIRARC activities shall be plan and conducted –
a. for situation –
i. where hazard appear to pose significant threat;
ii. uncertain whether existing controls are adequate; or/and
iii. before implementing corrective or preventive measures.
b. by organization intending to continuously improve Occupational Safety and Health (OSH) Management System.
When / Where to apply?
HAZARD IDENTIFICATION, RISK ASSESSMENT AND RISK CONTROL
(HIRARC)
Basic Component of Risk Management
Hazard Identification
Risk Assessment
Risk Control
Review
Hazard Identification
Sources of Hazards
• Man – Human behavior, Unsafe Act • Machinery – Installation, layout and design of
equipment • Materials – substances such as chemicals and gases
use in the workplace • Method – the way people carry out their work • Medium – workplace condition i.e. air quality,
ventilation, lighting, noise, vibration etc
Methods of Identifying Hazards
• Document Review: • Incident records • Monitoring records • Medical surveillance records
• Workplace Inspection • Hazard at workplace (existing &
potential) • Existing control (engineering,
administrative, PPE)
Risk Assessment
Risk Assessment Approaches
Determining Severity and Likelihood of Hazard Occurrence in three types of approach:
•Quantitative •Semi – Quantitative •Qualitative
Determining Severity
Severity in terms of: • Harm to health • Damage to property • Damage to environment • Or combination of above
Determining Likelihood
Likelihood of hazard occurring based on:
• Number of times activities performed
• Number of times of hazard occurrences
Severity Level
1. QUANTITATIVE RISK ASSESSMENT APPROACH
Likelihood Level
Example of risk matrix
Priority Action
SEVERITY LIKELIHOOD
Highly unlikely
Unlikely Likely Highly Likely
Negligible Low Low Medium Medium
Minor Low Medium Medium High
Major Medium Medium Medium High
Fatality Medium High High High
2. QUALITATIVE RISK ASSESSMENT APPROACH
3. SEMI-QUANTITATIVE RISK ASSESSMENT APPROACH
SEVERITY LIKELIHOOD
Yearly Monthly Weekly Daily
1 2 3 4
First Aid and Near Misses
1 1 2 3 4
Less than or 4 days MC
2 2 4 6 8
More than 4 days MC
3 3 6 9 12
Fatality & Permanent disability
4 4 8 12 16
Decision For Action
Risk level action and timescale • Trivial
• No action is required and no documentary records need to be kept
• Moderate • Effort should be made to reduce the risk. Risk reduction
measure should be implemented within a defined time period
• Intolerable • Work should not be started or continued until the risk has
been reduced. If it is not possible to reduce risk even with unlimited resources, work has to remain prohibited
Risk Control
Consideration in Implementing Risk Control
• Review measures regularly; modify if necessary
• Comply with national laws and regulations
• Reflect good management practice • Consider the current stage of knowledge • Include information or reports from
organizations such as DOSH and others
Hierarchy of Control
• Most effective • Elimination
• Fairly Effective • Substitution • Isolation • Engineering control
• Least effective • Administration Control • PPE
Types of Control 1. Engineering control modifying, redesigning or replacing:
•work stations and work areas
•materials/objects/containers design and handling
•hand tools & equipment
•Ventilation system
•Process flow
•Automation
3. PPE
•last resort when neither engineering nor administrative controls are possible, or in the event of emergencies
•PPE simply reduces the amount of hazardous exposure by placing a barrier between the hazard and the worker.
2. Administrative control •Proper maintenance and housekeeping
•Job rotation and enlargement
•Work scheduling
•Sufficient breaks
•Work practice
•Training
Process flow of HIRARC implementation
Hazard Identification • List down the steps to complete a
task • identify possibility of hazard in
every step • List down the hazards
Risk Assessment • List down safety control available
(eg: Emergency switch, SOP, fire ext) at the workplace
• Determine the existing type of control
-Eliminate -Replace -Engineering Control -Administrative control -PPE
• Assessment • Scoring
Risk Control
• List down the new/ additional safety control required
• Refer to hierarchy of control • Priority must be given to
engineering control. PPE the last choice
• Finalize
Example HIRARC
QUIZ#2 First-year students are required to take basic engineering skills class, which involves the sheet metal forming workshop. In this session, each students are required to fabricate a tool box made of Aluminum sheets. Prepare HIRRC analysis to access the possible hazards and risks for this workshop
No Work activities 1 Retrieving aluminum sheet from container 2. Measuring and dimension marking using steel rulers and scrapers 3. Shearing with shearing machine 4. Cutting with scissors 5. Bending ( hammer, anvil, clamp, shearing machine) 6. Assembling parts (with hammer, anvil, pliers) 7. Indenting(hammer, indenter) 8. Drilling(hand drill, g clamp, pliers) 9. Riveting (hand rivet, nails) 10 Housekeeping (arrange tools, sweep off the chips, cleaning the
machine)
2 Fault Tree Analysis
Fault-Tree Analysis -Fault – tree analysis concentrate on the end result, which is usually an accident or some other adverse consequence. -Accident are caused at least as often by the procedural errors as by equipment failures, and fault-tree analysis consider all cases; procedural and equipment. -The term fault tree arises from the appearance of the logic diagram that is used to analyze the probabilities associated with the various causes and their effects. -The leaves and branches of the fault tree are the myriad individual circumstances or events that can contribute to an accident.
-The base or trunk of the tree is the catastrophic accident or other undesirable result being studied.
OR gate
AND gate
Top event Intermediate event
Basic event
Undeveloped event
External or house event
Transfer IN-OUT
FTA Logic and Event Symbols Fault-Tree Analysis
Fault Tree
• Fault tree: top-down approach starting with the unwanted consequences as the top event & identifying all factors that could contribute to the top event.
• Used to think through possible causes of a loss, to find most probable sequence of events leading to the loss & to quantify the probability of loss.
Fault-Tree Analysis
Steps: Fault Tree
To draw a fault tree take the following steps:
1. Determine undesirable event, which is to be the Top Event.
2. Determine the Basic Events, which could immediately cause the Top Event.
3. Determine the relationship between the Basic Events and the Top Event in terms of AND and OR gates.
4. Determine whether any of the Basic Events need further analysis, if so repeat steps 2 & 3.
Fault-Tree Analysis
EXAMPLE1 • AND Gate Example Consider a system with two components A and
B. The system fails if both A and B fail. Draw the fault tree diagram for the system.
EXAMPLE2
• OR Gate Example Consider a system with three components A, B
and C. The system fails if either A, B or C fails. Draw the fault tree block diagram for the system.
Example 3
Consider a case of a overheated motor. The Basic Events could be the primary motor fails or excessive current load to the motor. The current load might be excessive due to excess current flow in the circuit and failure of the fuse. It could be either short circuiting or a power surge that contributed to the excess current flow.
Example: Fault Tree Motor Overheated
Primary Motor Failure
A
Fuse Fails
B
Excessive Current to Motor
Excess Current In Circuit
Short circuit
C
Power Surge
D
AND
OR
OR
The probability of the Top Event (the motor overheated) is obtained by combining the base events according to the logic rules:
For this case, probability
= [(C+D) x B] + A
For an OR gate (ADD the probabilities)
For an AND gate (MULTIPLY the value)
SOLUTION Motor Overheated
Primary Motor Failure
0.05
Fuse Fails
0.1
Excessive Current to Motor
Excess Current In Circuit
Short circuit
0.007
Power Surge
0.003
AND
OR
OR
The probability of the Top Event (the motor overheated) is obtained by combining the base events according to the logic rules:
For this case, probability of motor overheated is:
= [(0.007+0.003) x 0.1] + 0.05
= 0.051
0.01
0.001
0.051
Fault-Tree Diagram
OR
AND AND AND
Fault-Tree Diagram - example
Example of Fault-tree analysis
QUIZ # 2 The Fire Protection System failed to function in the recent fire tragedy in Company XYZ . The case could be caused by either failure of Fire Detection System or Water Deluge System failure. The Fire Detection System failure could be resulted from smoke detector malfunction and heat detector malfunction, while the Water Deluge System Failure probably caused by pump malfunction or blocked nozzles. The probability of occurrences of each event is listed below: •Smoke detector fail = 0.06 •Heat detector fail = 0.04 •Pump fail = 0.007 •Nozzle fail = 0.01 Based on the case study, construct a Fault Tree Analysis. Calculate the probability of Fire Protection System failure
3 Event Tree Analysis
— Graphical model that identifies possible outcomes from a given initiating event.
— Suited for complex processes involving several layers of safety systems.
— First: Identify an initiating event that could lead to failure of the system (e.g. human error, utility failure etc.)
— Second: Identify intermediate events/action which resulted from the initiating event (usually are safety features).
— Each intermediate event leads to two branches, one for a successful, and the other for an unsuccessful operation.
Event Tree Analysis
• To analyse risk of possible consequences of an initiating event or failure
• Starting with initiating event which might produce variety of consequences depending on subsequent event
• Can be used to investigate the feasible outcome of an event and estimate relative probability of each outcome
Event Tree Analysis
1st step: Initiating event column.
2nd step: Subsequent events (usually branches in to 2 paths (YES it will happen or NO it won’t). These events might be more than one, hence need to list all.
3rd step: Two columns drawn for overall outcome/consequence and to calculate its probability.
Event Tree Analysis
An Event Tree Analysis for a Fluid Flow Problem
P-2 Fails
Low Flow Alarm Sounds 0.998
Operator Responds OK 0.952
P-1 Starts 0.995
System Success
X
N
Y
Y
Y
N
N
0.945 Y
0.005 N
0.048 N
0.002 N
Total 1.00
Example 2 Consider the event of a steering wheel failure (initiating event).
Suppose that there is a 50% chance that the driver is able to counter the failure and control the steering safely.
If he/she cannot correct the failure, there may be a collision with another car. There is also the possibility that driver himself might crash into the steering wheel upon impact.
The probability of a collision with another car is 0.2 and the probability of the driver crashing into the steering wheel is 0.3.
Construct an event tree to determine the probabilities of events that could occur should there be a steering wheel failure.
Event Tree Analysis
A B C Consequences Probability
Correct Avoid Avoid
Steering Collision Injury
YES
A’ = 0.5 NO
B’ = 0.2 NO
B = 0.8 YES
YES C = 0.7
NO C’ = 0.3
NO C’ = 0.3
YES C = 0.7
STEERING
FAILS
Collision Avoided
Collision Avoided
Injury to Self
Collision
Collision + Injury
0.50
0.28
0.12
0.07
0.03
1.00
Example: Event Tree
Able to control the
steering
Fail to control
Collision occur
Avoid collision
Only collision,
no injury
Collision occur+ driver injured
Example 3 TUTORIAL
Tutorial 3 • Numbers of explosions case forecasted to be
happen in various industries in the USA annually. 80% of the explosions are expected to set up fire.
• Based on this data, every industries installed excellent Fire Alarm System at their place so that the reliability of the sprinkler to function is 99% and the probability of alarm not activated is 0.1%
• Construct an event tree to determine the Consequences & Probabilities of events that could occur from a case of explosion.
0.01x0.1
1-0.001
Exercise Consider the event of a forklift’s crane failure (initiating event).
Mr. D is retracting the forklift’s fork to store overload items at a storage located 20 feet from ground. Suddenly the forklift’s crane fails. Suppose that there is a 40% chance that the driver is able to retract the fork safely.
If he fail to do so, the items which the forklift is carrying will drop on to the ground. There is also the possibility that crane might crash on to the driver.
The probability of dropping the item is 0.6 and the probability of the crane hit the driver is 0.45.
Construct an event tree to determine the probabilities of events that could occur from a forklift crane failure.
Questions??
What are the differences between a fault tree and an event tree?
What are the advantages or
disadvantages of the fault tree or event tree methods?
DAH HABIS
Thank You
To be continued on next lecture
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