QRA for IOCL’s LPG Bottling Plant, Dimapur, Nagaland

Indian Oil Corporation Ltd (IOCL) operates an LPG bottling plant at Dimapur, Nagaland, storing product in two above-ground bullets of 33 MT capacity each and two mounded bullets of 150 MT capacity each, alongside one carousel filling line, two tank-truck unloading bays, one tank-truck loading bay, and dedicated packed-truck loading and unloading points. iFluids Engineering carried out a Quantitative Risk Assessment (QRA) for this facility to identify credible Loss of Containment (LOC) scenarios and confirm the plant’s risk profile against the UK Health and Safety Executive’s (HSE) risk acceptance criteria under the ALARP (As Low As Reasonably Practicable) principle. Northeast India’s LPG supply chain runs through a small number of bottling plants, and Dimapur keeps cylinder and bulk distribution moving across Nagaland and neighbouring Assam districts. A QRA at this scale of plant determines whether that supply role can continue without exposing personnel or the surrounding area to risk levels a regulator would not accept.

Field	Detail
Sector	Oil & Gas (LPG Distribution)
Location	Dimapur, Nagaland, India
Facility Type	LPG bottling plant: 2 above-ground bullets, 2 mounded bullets, 1 carousel
Client	Indian Oil Corporation Ltd (IOCL)
Scope of Work	Quantitative Risk Assessment (QRA)
Standards / Criteria Applied	UK HSE risk acceptance criteria, ALARP principle, OISD-STD-150
Regulatory Framework	PNGRB authorisation requirements for LPG bottling plants
Project Duration	Not publicly disclosed for this engagement
iFluids Team Size	Not publicly disclosed for this engagement

The Engineering Challenge at IOCL’s Dimapur LPG Bottling Plant

IOCL’s Dimapur bottling plant handles LPG storage and transfer at a scale where a single mounded-bullet or carousel failure could expose personnel, the public, and adjoining infrastructure to fire and blast hazards a regulator requires to be identified and reduced to ALARP levels before the plant can keep operating.

The plant’s four storage bullets, its carousel, and its four transfer points each carry a distinct set of credible LOC scenarios. A ruptured hose at the packed-truck loading point behaves differently from a flanged-joint leak on a mounded bullet, and a QRA has to model jet fire, pool fire, flash fire, vapour cloud dispersion, and BLEVE (boiling liquid expanding vapour explosion) separately for each. PNGRB requires an operator to complete a Quantitative Risk Assessment, HAZOP study, and Emergency Response and Disaster Management Plan before it will authorise an LPG bottling plant to operate. That authorisation requirement is what turns the QRA from a technical exercise into a condition of the plant staying in business.

Consequence severity also depends on domino potential: a jet fire from a bay hose failure can escalate into a bullet failure if flame impingement lasts long enough, converting a moderate-consequence transfer-point incident into a catastrophic storage-vessel event. A QRA has to model that escalation pathway explicitly rather than treating each LOC scenario as independent, because the credible worst case at a bottling plant is rarely the largest vessel failing on its own.

iFluids’ QRA Approach and Methodology

iFluids Engineering’s Quantitative Risk Assessment (QRA) service identifies Loss of Containment scenarios, quantifies their consequence and frequency, and benchmarks the resulting individual and societal risk against the UK HSE’s risk acceptance criteria under ALARP, producing a risk register a plant operator and its regulator can act on.

The methodology followed a standard sequence for the Dimapur facility:

1. Hazard identification: catalogue every credible LOC scenario across the bullets, carousel, bays, and packed-load points.
2. Consequence modelling: quantify jet fire, pool fire, flash fire, vapour cloud dispersion, and BLEVE effect distances for each scenario.
3. Frequency analysis: assign failure frequencies to each LOC scenario using recognised process industry failure-rate data.
4. Risk quantification: combine consequence and frequency into individual risk contours around the plant and a societal risk (F-N curve) profile.
5. ALARP evaluation: compare the calculated risk levels against the applicable acceptance criteria.
6. Risk reduction recommendations: where a scenario sits outside the acceptable band, recommend engineering or procedural mitigation.

The UK HSE’s tolerability-of-risk framework defines an individual risk above 1 in 10,000 per year to a member of the public as unacceptable and a risk below 1 in 1,000,000 per year as broadly acceptable, leaving the ALARP principle to govern the region between those two limits. That three-tier structure is what gives a QRA’s output a clear pass, ALARP, or fail signal instead of a vague hazard rating.

Societal risk is presented as an F-N curve, plotting the frequency of an incident against the number of people it could affect, so a scenario capable of harming many people at low frequency can be compared directly against one capable of harming fewer people more often. Consequence distances for vapour cloud dispersion also depend on atmospheric stability class and wind speed, both selected from meteorological data representative of the plant’s location rather than a single generic weather assumption.

Technical Decisions and Engineering Rationale

Dimapur’s mix of above-ground and mounded LPG bullets shapes the entire QRA scope: mounded vessels covered under OISD-STD-150 reduce fireball and BLEVE escalation risk through earth cover, and that design choice changes which scenarios drive the plant’s individual and societal risk profile.

OISD-STD-150 specifies minimum earth-cover thickness and vapour-relief venting arrangements for mounded LPG vessels to limit heat transfer from an external fire and reduce the likelihood of a BLEVE, sitting alongside the broader hazardous area classification standards (IEC, ATEX, NEC, OISD) that govern equipment selection around the same vessels. That is a materially different failure path from the plant’s two above-ground 33 MT bullets, where direct flame impingement and jet fire escalation dominate instead. The carousel and the loading and unloading bays introduce a third category entirely: LOC scenarios tied to hose, arm, and coupling failure during active product transfer, which typically occur far more often than a catastrophic vessel failure but at a smaller consequence radius. Separating these three failure populations, rather than modelling the whole site as one generic “LPG storage” hazard, is what let the QRA attribute individual and societal risk to the parts of the plant actually driving it. A single combined hazard model would have obscured which asset, the bullets, the carousel, or the bays, needed a recommendation.

OISD-STD-150 also sets minimum separation distances between a mounded bullet and other plant equipment, a requirement that directly limits how close the carousel and above-ground bullets can sit to the mounded vessels without triggering a domino assessment. Where transfer infrastructure sits near mounded bullets, a QRA has to check that separation compliance explicitly rather than assume it from the vessel type alone.

Outcomes and Deliverables

The QRA gave IOCL a documented risk register benchmarking the Dimapur plant’s bullets, carousel, and bay operations for individual and societal risk against UK HSE acceptance criteria, with the ALARP demonstration and any risk-reduction recommendations needed to support PNGRB authorisation and continued safe operation.

Deliverable	Standard / Criteria	Outcome
QRA report (LOC identification, consequence and frequency analysis)	UK HSE risk acceptance criteria	Individual and societal risk quantified for the bullets, carousel, and transfer points
ALARP demonstration	ALARP principle	Risk levels benchmarked against the acceptable, ALARP, and unacceptable bands
Risk reduction recommendations register	PNGRB / OISD-STD-150	Mitigation measures identified for any scenario falling outside the acceptable band

PNGRB requires an LPG bottling plant operator to close out QRA-driven risk-reduction recommendations as a condition of retaining its authorisation to operate, which is why the recommendations register is treated as a compliance deliverable rather than a supplementary suggestion.

Lessons and Applicability for Northeast India LPG Facilities

Bottling plants across India’s LPG distribution network, including IOCL’s LPG bottling plant at Belgaum, Karnataka that iFluids has also assessed, show a pattern worth generalising from Dimapur: transfer points, not bulk storage vessels, tend to generate the highest-frequency LOC scenarios, even where storage carries the largest consequence.

For a Northeast India facility specifically, that pattern matters because supply routes into the region run through a limited number of corridors, and an unplanned shutdown at a single bottling plant has fewer nearby alternates to absorb the gap than a plant on the mainland grid would have. A QRA that correctly attributes risk to the carousel and bays, not just the bullets, gives an operator a maintenance and inspection priority list that matches where failures actually originate. The same logic applies to any bottling plant combining above-ground and mounded storage: OISD-STD-150 compliance on the mounded vessels addresses one risk driver, but it does not substitute for separately assessing the transfer infrastructure.

Hill terrain adds a variable a flat-terrain QRA template rarely addresses: valley and ridge topography around a Northeast India site can channel a dense vapour cloud along a drainage path instead of letting it disperse evenly downwind, changing the individual risk contour shape compared with a flat-terrain plant. OISD-STD-150 governs mounded-vessel design uniformly across regions, but it does not specify terrain-based dispersion behaviour, so that assessment falls to site-specific meteorological input the QRA has to gather independently. Any bottling plant sited on similar terrain should treat flat-terrain dispersion assumptions as a starting point to verify, not a substitute for site-specific modelling.

Conclusion and Next Steps

iFluids Engineering’s QRA for IOCL’s Dimapur LPG bottling plant benchmarked the facility’s above-ground and mounded storage, carousel, and bay operations against UK HSE risk acceptance criteria and closed the ALARP loop PNGRB requires before authorising continued operation. This project is representative of iFluids’ work for LPG bottling and bulk storage operators across India who need a defensible, standards-referenced risk assessment rather than a generic hazard checklist. If your facility needs a Quantitative Risk Assessment benchmarked against UK HSE, OISD, or PNGRB criteria, contact iFluids Engineering to discuss scope.