Frequently Asked Questions

A HAZOP (Hazard and Operability) study is a structured, team-based technique that systematically examines a process using guide words applied to parameters at each P&ID node to identify deviations, their causes, consequences, and existing safeguards.

A trained and experienced HAZOP facilitator (chairman), independent of the design team, leads the study to ensure objectivity, supported by a scribe who records findings in real time.

Industry practice and many regulatory frameworks recommend HAZOP revalidation every 5 years, or sooner if significant process or equipment changes have occurred since the last study.

HAZID (Hazard Identification) is a qualitative, early-stage hazard identification technique performed at concept or pre-FEED stage to identify major hazards related to a facility and its site before detailed design begins.

A HAZID study produces a hazard register listing identified hazards, their screening outcome, and recommendations — including which scenarios warrant further quantitative study such as QRA.

SIL stands for Safety Integrity Level, a measure defined in IEC 61508/61511 of the reliability required of a safety instrumented function, ranked from SIL 1 (lowest) to SIL 4 (highest risk reduction).

PFDavg (Probability of Failure on Demand, average) is the calculated average probability that a safety instrumented function will fail to perform its safety action when called upon — the key metric used to verify a SIF meets its target SIL.

It depends on the sensor's certified failure data and the overall architecture (1oo1, 1oo2, 2oo3 etc.); a single non-redundant element rarely achieves SIL 3 alone unless its certified PFD and architectural constraints (per IEC 61511) support it.

LOPA is used to evaluate whether the independent protection layers (IPLs) safeguarding a hazard scenario provide sufficient risk reduction, bridging qualitative HAZOP findings and quantitative SIL determination.

An IPL is a device, system, or action capable of preventing a scenario from proceeding to its undesired consequence, independent of the initiating event and of other IPLs credited for the same scenario.

Quantitative Risk Assessment (QRA) is a numerical risk assessment methodology combining failure frequency data and consequence modelling to calculate individual risk and societal risk (F-N curves) for a facility's major hazard scenarios.

An F-N curve plots cumulative frequency (F) against the number of fatalities (N) for a facility's hazard scenarios, used to assess societal risk against tolerability criteria.

Individual risk is the calculated annual probability that a specific person, located at a specific point, will be killed as a result of an accident arising from hazardous activities at a facility.

ALARP (As Low As Reasonably Practicable) is a risk tolerability principle stating risk should be reduced until further reduction costs are grossly disproportionate to the safety benefit gained.

ALARP is demonstrated by showing that all reasonably practicable risk reduction measures have been implemented, typically through a cost-benefit analysis comparing the cost of additional safeguards against the quantified risk reduction achieved.

Consequence modelling is the quantitative simulation of physical effects — dispersion, fire, and explosion — from a loss-of-containment event, producing hazard footprint distances used in QRA and emergency planning.

The source term is the release rate, duration, and phase (gas, liquid, two-phase) of material escaping during a loss-of-containment event — the critical input determining accuracy of all downstream consequence modelling.

A jet fire results from the ignition of a pressurised, momentum-driven release (gas or two-phase), producing a directional flame; a pool fire results from ignition of a liquid pool that has accumulated on a surface, producing a roughly vertical flame above the pool.

Process Safety Management (PSM) is a structured management system of interrelated elements — covering process knowledge, hazard analysis, procedures, training, mechanical integrity, and management of change — designed to prevent catastrophic chemical releases.

The CCPS Risk-Based Process Safety (RBPS) framework defines 20 elements organised under four pillars: Commit to Process Safety, Understand Hazards and Risk, Manage Risk, and Learn from Experience.

Management of Change is a PSM element requiring systematic review and authorisation of any change to process technology, equipment, procedures, or personnel before implementation, to ensure new hazards are identified and controlled.

ERDMP (Emergency Response and Disaster Management Plan) is a statutory document required under India's MSIHC Rules, 1989 for Major Accident Hazard units, detailing on-site and off-site emergency response and coordination arrangements.

The on-site emergency plan covers response arrangements within the facility boundary, managed by the occupier; the off-site emergency plan covers response coordination beyond the boundary, prepared by the District Disaster Management Authority using the occupier's on-site plan and hazard data as input.

Risk Based Inspection (RBI) is a methodology, per API 580/581, that prioritises inspection resources and intervals based on the calculated risk (probability x consequence) of failure for each equipment item.

API 580 sets out the qualitative/semi-quantitative RBI methodology and program management framework; API 581 provides the detailed quantitative risk calculation methodology used to implement an API 580-aligned program.

Bow-Tie Analysis is a visual risk assessment method that maps the threats (causes) leading to a top event and the consequences flowing from it, alongside the preventive and mitigative barriers controlling each pathway.

A barrier in Bow-Tie analysis is any control — physical, procedural, or human-action — that prevents a threat from causing the top event (preventive barrier) or limits the consequences once the top event occurs (mitigative barrier).

Thermal hazard testing uses calorimetric techniques such as DSC and adiabatic calorimetry to measure a chemical reaction's exothermic onset temperature, adiabatic temperature rise, and decomposition energy, identifying runaway reaction risk before it occurs at plant scale.

Differential Scanning Calorimetry (DSC) is used as a rapid screening test to detect exothermic or decomposition events in a small sample and estimate the onset temperature at which a reaction mixture becomes thermally unstable.

TMRad (Time to Maximum Rate under adiabatic conditions) is the time it would take a reaction mixture to reach its maximum self-heating rate if held adiabatically at a given temperature — a key input for setting safe holding times after a cooling failure.

HAZID is performed early at concept/pre-FEED stage at a coarse, facility-wide level; HAZOP is performed later once P&IDs exist, examining process deviations node-by-node in much finer detail.

An MAH unit is a facility that stores or handles hazardous chemicals above threshold quantities specified under India's MSIHC Rules, 1989, triggering additional statutory obligations including safety reports and ERDMP.

Comprehensive process safety audits are typically conducted every 1-3 years depending on hazard category, regulatory requirement, and corporate policy, supplemented by more frequent internal inspections.