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?

Summary

End of Lecture

DAH HABIS

Thank You

To be continued on next lecture