[FC] TOPIC 5: Hazards Analysis Methods

HAZOP stands for?

• HAZ — Hazard    ||    OP — Operability

• Hazard — any deviation in operation that can cause:

  • a release of toxic, flammable or explosive chemicals, or

  • any action that could result in injury to personnel

• Operability — any deviation in operation within the design envelope that will cause:

  • a shutdown or

  • lead to a violation of environmental, health or safety regulations, or

  • negatively impact profitability

What is HAZOP?

• A systematic process hazard analysis technique to IDENTIFY potential hazard & operating problems

• Conducted by a multi-disciplinary team using qualitative technique based on "guidewords" to uncover deviations

  • Guidewords help to detect how deviations can lead to hazardous situations or operability problems

Purpose of HAZOP

• Identify deviations from design/normal operations and uncover associated hazards and operability problems

• Generate corrective actions to eliminate risks of these deviations that result in hazardous consequences or operability problems or reduce them to acceptable levels

When to conduct HAZOP and follow-ups?

• Design Phase — When P&IDs reach ‘Approved for Design’ stage

• Construction Site Inspections — Verify HAZOP recommendations are implemented

• Pre-Commissioning — Conduct safety reviews plant procedures & safety audits

• Operational Phase — Regular reviews (every 5 years) and after modifications to ensure continued safety

HAZOP study team

• HAZOP study team should consist of:

  • Typically consists of 5-8 people with a range of relevant skills

  • Independent leader (not from the plant being studied)

  • Project engineer

  • Operations representative

  • Discipline engineers

    • Process

    • Instrument/ electrical

    • Mechanical/ maintenance

  • HAZOP minute recorder

    • One of the above

What information does HAZOP require?

• HAZOP requires the following information:

  • P&IDs

  • Process flow diagrams

  • Heat and material balances

  • Layouts

  • Interlock logic diagrams

  • Equipment data sheets

  • Safety data sheets

  • Hazardous area layouts

What modes of operation does HAZOP consider?

• Modes of operation to be considered during HAZOP study:

  • Normal operation

  • Reduced throughput operation

  • Routine start-up

  • Routine shut-down

  • Emergency shutdown

  • Commissioning

  • Special operating modes

Principle of HAZOP — flow

Preventive Actions		Mitigation Actions
↑		↑
Identify Causes	← PARAMETER →	Identify Consequences

Principle of HAZOP — Guidewords, meanings and examples

GUIDEWORDS	MEANING	EXAMPLES / DEVIATION
No (not, none)	None of the design intent is achieved	No flow when production is expected
More (more of, higher)	Quantitative increase in a parameter	Higher temperature than desired
Less (less of, lower)	Quantitative decrease in a parameter	Lower pressure than normal
As well as (more than)	An additional activity occurs	Other valves closed at the same time (logic fault or human error)
Part of	Only some of the design intention is achieved	Only part of the system is shut down
Reverse	Opposite of the design intention occurs	Back-flow when the system shuts down
Other than (other)	Complete substitution as another activity takes place	Liquids in the gas piping
Early / late	The timing is different from the intention	-
Before / after	The step (or part of it) is effected out of sequence	-
Faster / slower	The step is done/not done with the right timing	-
Where else	Applicable for flows, transfer, sources and destinations	-

Principle of HAZOP — Examples of parameters

Flow Pressure Temperature Mixing Stirring Transfer Level Viscosity Reaction

Composition Addition Separation Time Phase Speed Particle size Measure Control

pH Sequence Signal  Start / stop Operate Maintain Service Communication Absorb

Principle of HAZOP — Examples of guidewords + parameter + eg. causes

• Examples of Guidewords + Parameters + (eg. causes)

  • No Flow (eg. wrong flow path, blockage, incorrect blind plate, incorrectly fitted check valve, burst pipe, large leak, equipment failure, incorrect pressure differential, isolation in error)

  • More Flow (eg. increased pumping capacity, increased suction pressure, reduced delivery head, greater fluid density, exchanger tube leaks, cross connection of systems, control faults)

  • More Temperature (eg. ambient conditions, failed exchanger tubes, fire situation, cooling water failure, defective control, internal fires)

What is Bow-Tie Analysis?

• Links Hazards & Consequences to an ‘Event’ which enables development of Causes & Threats and Preventive & Recovery measures

• Effective visualisation & better communication of hazards

What are the steps for Bow-Tie Analysis?

(1. Hazard)

2. Top Event

3. Consequence

4. Threat

5. Barriers

6. Recovery Measures

7. Escalation Factors & Controls

8. Critical Tasks

Bow-Tie Analysis — Hazard

1. Hazard — Anything, any source or any situation with the potential to cause:

• Bodily injury, ill-health or death

• Damage to equipment or properties

• Delay to operations or work schedules

Bow-Tie Analysis — Top Event

2. Top Event — The incident that occurs as a result of a hazard being released

• eg. Loss of containment

• Electrical shock

• Fall from height

• Exposure to toxic material

• Exposure to radioactive material

• Effluent discharge into waterways

• Emission of toxic gases

Bow-Tie Analysis — Consequence

3. Consequence — An event or chain of events that results from the hazard being released

• eg. Serious injury

• Death

• Latent illness or disease which has long gestation period (Chronic illnesses)

• Property damage (ie. own or public)

• Environmental damage

• Loss of reputation leading to loss in current & prospective business

• Loss of revenue - paying for compensation, medical expenses, production loss or deferment

Bow-Tie Analysis — Threat

4. Threat — A possible cause that will release the hazard to become a top event

• eg. Threat → Top Event

• Corrosion/erosion of pipes → Loss of containment

• Loose electrical wiring → Electrical shock/fire

• Over-pressurisation of a vessel → Explosion

• Incorrect valve positioning → Toxic gas release

• Fatigue/lack of training → Incorrect operation of equipment

• Extreme weather (eg. lightning) → Power surge/fire

Bow-Tie Analysis — Barriers

5. Barriers — Measures put in to prevent the release of a hazard or to prevent the occurrence of a top event once the hazard is released

• eg. Guards or protective shields e.g. protective coatings, corrosion inhibitors, machine guards, fencing etc.

• Pressure / safety relief valves

• High temperature cut-off switches

• Correct / valid / updated operating procedures

• Safety interlocks in processes

• Lowering speeds of equipment

• Carry out maintenance when it is due

• Reducing congestion in operating areas

Bow-Tie Analysis — Recovery Measures

6. Recovery Measures — All technical, operational, & organizational measures to reduce the impact of the Consequences due to the occurrence of the Top Event

• eg. Gas, fire & smoke alarms

• Emergency Shutdown systems

• Firewater deluge systems

• Fire and blast walls

• Emergency Response plans, training & drills

• Business Resumption Plans

Bow-Tie Analysis — Escalation Factors & Controls

7. Escalation Factors & Controls — Conditions that lead to increased risk due to loss of barriers or loss of recovery measures especially life saving or mitigating capabilities. Escalation Controls can then be identified for Escalation Factors.

• eg. Abnormal operating condition (such as critical standby equipment is under maintenance during an emergency)

• Plant operating outside the design envelope

• Extreme environmental conditions - may not allow the activation of planned recovery measures

• Incorrect operation of the plant due to unavailability of updated operating procedures

• Human error due to lack of competence or ineffective training

Bow-Tie Analysis — Critical Tasks

8. Critical Tasks — Activities that need to be carried out to ensure the effectiveness and correct operation of Barriers and Recovery Measures