OISD vs ISA TR84.00.07: Reconciling Fire and Gas Mapping Requirements in India

OISD-116, published by India’s Oil Industry Safety Directorate, sets prescriptive design rules for fire and gas detection and alarm systems at refineries and gas processing plants. ISA TR84.00.07, issued by the International Society of Automation, defines a performance-based methodology for verifying that a fire and gas system actually detects credible release scenarios. Projects in India routinely need both: OISD compliance to satisfy the statutory audit, and an ISA TR84.00.07 mapping study to demonstrate the detector layout achieves adequate coverage.

This creates a practical question for process safety and instrumentation engineers: which standard sets the baseline, and which one verifies the result? OISD-116 answers what must be installed. ISA TR84.00.07 answers whether what’s installed actually works. Treating OISD and ISA TR84.00.07 as competing standards, rather than sequential layers, is the most common design error on India-linked fire and gas mapping projects. This article maps the scope of each standard, shows where their requirements overlap, and outlines how a single mapping study satisfies both.

What Is Fire and Gas Mapping Under OISD and ISA TR84.00.07

OISD-116 and ISA TR84.00.07 govern fire and gas mapping from two different directions: OISD prescribes minimum detector types, spacing, and alarm philosophy for Indian oil and gas facilities, while ISA TR84.00.07 calculates scenario and geographic coverage using dispersion and flame-detection modelling. Together they define both the design baseline and the performance verification for a fire and gas system.

OISD was established in 1986 under India’s Ministry of Petroleum and Natural Gas, and OISD-116 covers fire protection facilities, including gas detection and alarm systems, for refineries and oil and gas processing plants. ISA TR84.00.07 grew out of a gap identified by the ISA 84 committee: IEC 61511’s safety instrumented function metrics assume detection and mitigation are close to binary, which does not hold for fire and gas systems, where coverage is never 100 percent and detection only reduces rather than prevents consequences. The technical report ISA TR84.00.07 defines scenario coverage and geographic coverage as the two core metrics for evaluating whether a detector array will actually catch a credible release before it escalates. A facility can be fully OISD-compliant on paper, with every prescribed detector type installed, and still fail an ISA TR84.00.07 coverage calculation if the detectors are not positioned against the plant’s actual release scenarios.

Scope and Applicability: Where OISD Governs and Where ISA TR84.00.07 Governs

OISD-116 applies mandatorily to refineries, gas processing plants, and associated facilities operating in India, while ISA TR84.00.07 applies as a voluntary methodology used globally, including inside India, to verify fire and gas system effectiveness once the OISD-driven design exists. OISD compliance is a statutory audit condition; ISA TR84.00.07 compliance is a client or corporate specification.

OISD-116 covers fire protection facilities within the refinery boundary, and it explicitly extends to petroleum depots, terminals, lube blending plants, and pipeline installations located outside the refinery when they sit under the same management and in close proximity. Facilities outside that boundary fall instead under OISD-STD-144 for LPG storage, handling, and bottling, or OISD-STD-150 for mounded storage. Hazardous area classification, which determines where flammable atmospheres can occur and therefore where detectors are even relevant, is separately governed by OISD-STD-113, covered in detail in iFluids’ hazardous area classification standards comparison. ISA TR84.00.07 carries no jurisdictional boundary of its own; it is applied wherever a client, insurer, or internal functional safety program requires demonstrated coverage, which in practice means most GCC, India, and Southeast Asia projects layer it on top of whichever local prescriptive code applies, OISD in India or NFPA and API RP 505 in the Gulf.

Key Requirements: Prescriptive OISD Clauses vs Performance-Based ISA TR84.00.07 Methodology

OISD-116 mandates specific gas detection and alarm provisions as a design input, while ISA TR84.00.07 calculates whether that input, once installed, achieves an acceptable probability of detecting a credible loss-of-containment event. The two operate sequentially: OISD sets the starting detector philosophy, and ISA TR84.00.07 tests and refines the layout against dispersion and flame-detection modelling.

OISD-116 Gas Detection and Alarm System Requirements

OISD-116 mandates minimum design criteria for gas detection and alarm systems at process units, tank farms, and loading facilities within refineries and gas processing plants. The standard specifies detector types and general placement philosophy tied to process area classification, and it requires alarm and shutdown interlocks to be integrated with the facility’s emergency shutdown logic, following the same fire and gas detector placement engineering rules that govern voting logic and siting more broadly. Facilities that install detectors to meet only the letter of OISD-116, without validating placement against actual release scenarios, commonly discover coverage gaps only after an ISA TR84.00.07 mapping study is run retroactively.

ISA TR84.00.07 Scenario and Geographic Coverage Methodology

ISA TR84.00.07 defines geographic coverage and scenario coverage as the two metrics used to quantify fire and gas detection performance for a given detector layout. Geographic coverage measures the physical area a detector array can sense; scenario coverage weights that area against the frequency, size, and location of credible releases modelled for the unit. A facility with high geographic coverage can still register low scenario coverage if detectors sit outside the zones where releases are most probable, which is why ISA TR84.00.07 treats scenario coverage as the more decision-relevant metric.

Comparison Point	OISD-116	ISA TR84.00.07
Nature	Prescriptive design standard	Performance-based methodology
Publishing body	Oil Industry Safety Directorate, India	International Society of Automation
Applicability	Mandatory for Indian refineries and gas plants	Voluntary, applied globally as verification layer
Core output	Detector type, spacing, alarm philosophy	Scenario coverage and geographic coverage percentages
Verification method	Statutory OISD audit	Dispersion and flame-detection modelling
Typical project role	Design baseline	Coverage validation and gap closure

Compliance in GCC, India, and Southeast Asia

India-based facilities must satisfy OISD-116 as a statutory condition and typically layer an ISA TR84.00.07 mapping study on top for coverage assurance, while GCC and Southeast Asia projects substitute NFPA, API RP 505, or client-specific standards for the prescriptive layer but retain ISA TR84.00.07 as the common performance methodology across regions. This layered structure lets a single engineering methodology serve multiple regulatory regimes.

PESO governs LPG, LNG, and petroleum-product-specific installations in India, operating alongside OISD for facilities that fall within its scope, which means a fire and gas mapping study for an Indian LPG bottling plant may need to demonstrate compliance with PESO’s requirements in addition to OISD-116. In the GCC, ADNOC, QatarEnergy, and Saudi Aramco specifications typically reference NFPA 72 and API RP 505 as the prescriptive layer, with ISA TR84.00.07 required as the coverage verification methodology on major capital projects. Southeast Asian operators generally follow a similar pattern, adopting NFPA or client-specific philosophy documents for design and ISA TR84.00.07 for verification. The practical implication for engineering teams working across these regions is that the coverage-calculation skillset built on an ISA TR84.00.07 study is fully portable, even though the prescriptive standard underneath it changes by country.

Common Non-Conformances and How to Address Them

The most frequent non-conformance is treating OISD-116 compliance as sufficient on its own, without running an ISA TR84.00.07 coverage check, which leaves scenario coverage gaps that only surface during an incident investigation or a client audit. A second common failure is running the ISA TR84.00.07 study first and retrofitting it to justify a detector count that does not match OISD’s prescribed minimums.

Undocumented deviation from OISD-116’s prescribed detector spacing, made to satisfy an ISA TR84.00.07 coverage target, invalidates the facility’s statutory compliance basis unless the deviation is formally justified and recorded through the facility’s management of change process. The corrective sequence has three steps: establish the OISD-116 baseline first, run the ISA TR84.00.07 scenario and geographic coverage calculation against that baseline, and document any deviation from OISD’s prescriptive spacing as a specific, approved exception rather than a silent substitution. Facilities that skip this documentation step often fail the next statutory OISD audit even when their actual detection performance, measured by ISA TR84.00.07 metrics, is stronger than a purely prescriptive layout would have achieved.

Implementation Roadmap for a Dual-Compliant Fire and Gas Mapping Study

A dual-compliant study sequences OISD-116’s prescriptive baseline first and layers the ISA TR84.00.07 coverage calculation on top, closing any gap through documented deviation rather than silent redesign. This sequence keeps the statutory audit trail intact while still delivering a performance-verified detector layout.

1. Establish the OISD-116 baseline: confirm detector types, spacing, and alarm philosophy against the process area’s hazard classification under OISD-STD-113
2. Model credible release scenarios: identify loss-of-containment sources, frequencies, and dispersion behaviour for the unit
3. Calculate ISA TR84.00.07 coverage: run geographic and scenario coverage against the OISD baseline layout
4. Identify and close gaps: add, relocate, or re-type detectors where coverage falls below the target
5. Document deviations formally: record any departure from OISD’s prescribed spacing through management of change
6. Issue the combined compliance package: OISD audit evidence plus the ISA TR84.00.07 coverage report

Conclusion

OISD-116 and ISA TR84.00.07 are not competing standards; they answer different questions in the same fire and gas mapping study. OISD sets the mandatory design baseline for Indian refineries and gas plants, and ISA TR84.00.07 verifies that the baseline actually detects the releases the facility is exposed to. The practical takeaway for engineering teams is sequencing: establish the OISD-116 baseline, run the ISA TR84.00.07 coverage calculation, and document any deviation formally rather than letting one standard silently override the other. Facilities that skip this sequencing typically discover the gap during an audit or, worse, during an incident investigation.

For projects that need both the statutory design basis and a performance-verified detector layout, iFluids Engineering’s fire and gas mapping study services combine OISD compliance with ISA TR84.00.07 coverage calculation in a single deliverable.

This work is typically scoped alongside iFluids’ broader process safety management services for facilities managing the full compliance program, not just the detector layout.