Sector·3 min read
Geothermal Power Plant (JES) Fire Safety
Geothermal power plants (JES) are 'fuel-free' renewable facilities, yet they carry two unique fire risks: the toxic and flammable hydrogen sulfide (H2S) and non-condensable gases released with the fluid coming from underground, and — especially in binary/ORC plants — the flammable organic working fluids such as isopentane/isobutane used to drive the turbine. This article covers geothermal fire safety on the common ground of NFPA 850 shared with other power plants: water spray/deluge for turbine-generator lubrication/hydraulic oil fire, gas detection and ventilation for H2S and non-condensable gases (NCG), ATEX area classification, leak detection and gas/foam suppression for the ORC fluid, plus transformer and cooling-tower protection.
A-Pro Engineering
Geothermal power plants (JES) are “fuel-free” renewable facilities, yet they carry two unique fire risks: the toxic and flammable H2S released with the fluid coming from underground, and — especially in binary plants — the flammable organic working fluid (isopentane/isobutane). This article covers geothermal fire safety on the common ground of NFPA 850 shared with other plants; it is the geothermal companion to our power plant (NFPA 850) article.
Risk profile: two critical differences
As in all plants, turbine-generator oil fire is common ground. Two differences set JES apart:
- H2S and non-condensable gases (NCG) — arrive with the geothermal fluid; toxic + flammable.
- Binary/ORC flammable organic fluid — isopentane/isobutane; fire-explosion risk in a leak.
Turbine-generator oil fire
The turbine’s lubrication and hydraulic oil can cause a serious fire when sprayed onto a hot surface. Per NFPA 850, automatic water spray (deluge) is applied for oil units and under-turbine zones. We covered water spray in a separate article.
H2S and non-condensable gases
Hydrogen sulfide (H2S) is the main component of the non-condensable gases; it is toxic even at low concentrations, also flammable, and being heavier than air it accumulates in low areas. Therefore:
- Fixed H2S gas detection + appropriate ventilation,
- Personal gas detectors for personnel,
- Processing/removal of non-condensable gases as part of the process design.
Important warning: H2S dulls the sense of smell at high concentrations — “no smell” does not mean safe.
Binary/ORC and the flammable fluid
In a binary-cycle plant the geothermal fluid does not go directly to the turbine; it vaporizes a second-cycle organic fluid (isopentane/isobutane) in a heat exchanger and the turbine is driven by this flammable hydrocarbon vapour. A leak creates a vapour cloud → fire/explosion risk. Protection:
- Selecting equipment to suit ATEX / explosive-atmosphere area classification — see our fire detection and ATEX article,
- Hydrocarbon gas/leak detection and adequate ventilation,
- Static/grounding and emergency shutdown (ESD),
- Where needed, gas- or foam-based suppression.
In foam selection, fluorine-free (F3/SFFF) solutions should be preferred; classic AFFF/AR-AFFF contains PFAS and is being restricted. We covered foam design in a separate article.
Transformer and cooling tower
- Transformer: If oil-filled it carries an oil-fire risk; a dry type is preferred, or on an oil-filled transformer water spray cooling, a secondary oil-containment pit, and separation/compartmentation are applied.
- Cooling tower: If it has flammable fill/body material it is protected with sprinklers.
- Cable galleries / control room: Early detection + appropriate suppression (clean agent / water-based).
Summary
Geothermal fire safety is built on the common ground of NFPA 850 with two critical differences: H2S/non-condensable gases (toxic + flammable → gas detection, ventilation) and the binary-cycle flammable organic fluid (isopentane/isobutane → ATEX, leak detection, gas/foam suppression). Water spray/deluge for turbine-generator oil fire, dry-type/water-spray + oil containment for the transformer, and sprinklers for the cooling tower complete it. Because of the weight of the invisible-gas risks, gas detection is at the heart of the design. We also covered which structure requires which system in our general article. At A-Pro Engineering we design detection, water spray/deluge, gas, and foam systems for geothermal plants in an integrated way; contact us for your project.
This content is for information purposes. Binding design must be produced project-by-project based on the actual conditions of the plant (steam/flash or binary cycle) and the editions of NFPA 850, the relevant gas-safety/ATEX standards, and BYKHY in force.
© 2027 A-Pro Mühendislik. This is original technical content produced by A-Pro Engineering; all rights reserved. Copying, reproducing or republishing it in whole or in part without attribution and permission is prohibited.
Frequently asked questions
Where does the fire risk in a geothermal plant come from?+
Although JES is 'fuel-free,' it carries fire/explosion risk from several sources. First, as in all power plants, the turbine-generator's lubrication and hydraulic oil — a flammable oil that can ignite on a hot surface. Second, the non-condensable gases released with the geothermal fluid coming from underground; the hydrogen sulfide (H2S) in them is both toxic and flammable. Third, and most distinctive, the flammable organic working fluids such as isopentane/isobutane used to drive the turbine in binary/ORC plants; in a leak these pose a fire and explosion risk. Transformer oil and cooling-tower fill material are also risk sources.
By what standard is a geothermal plant protected?+
There is no separate mandatory international fire standard for geothermal plants; the most common reference for electric generating plants is NFPA 850 (Recommended Practice for Fire Protection for Electric Generating Plants). NFPA 850 covers the protection of common areas such as the turbine-generator, oil systems, transformer, cable galleries, and control room. To this are added the geothermal-specific H2S/non-condensable gas management and — in binary plants — ATEX/explosive-atmosphere and process-safety approaches for the flammable organic (ORC) fluid. In Türkiye, design falls within the scope of BYKHY and OHS legislation.
Why is H2S (hydrogen sulfide) important?+
Hydrogen sulfide is one of the main components of the non-condensable gases arriving with the geothermal fluid; it is toxic even at low concentrations and is also flammable, and because it is heavier than air it can accumulate in pits/low areas. A fixed H2S gas-detection system, appropriate ventilation, and personal gas detectors for personnel are therefore critical in JES. Detection is needed both for life safety (poisoning warning and evacuation) and for early recognition of flammable accumulation. Processing/removal of the non-condensable gases is part of the process design.
What is the extra risk in a binary/ORC plant?+
In a binary-cycle plant the geothermal fluid, rather than being sent directly to the turbine, vaporizes a second-cycle organic fluid (e.g., isopentane, isobutane) in a heat exchanger; the turbine is driven by this flammable hydrocarbon vapour. These fluids ignite easily and, in a leak, form a vapour cloud that creates a fire and explosion risk. Protection is provided by selecting equipment to suit ATEX/explosive-atmosphere area classification, hydrocarbon gas/leak detection, adequate ventilation, static/grounding, emergency shutdown (ESD), and, where needed, gas- or foam-based suppression. This is the most important difference that sets JES apart from a classic steam plant.
How are the turbine and transformer protected?+
The turbine-generator's lubrication and hydraulic oil can cause a serious fire when sprayed onto a hot surface; per NFPA 850, automatic water spray (deluge) systems are applied for oil units, batteries, and under-turbine zones. If power transformers are oil-filled they carry an oil-fire risk; a dry type is preferred, or on an oil-filled transformer water spray cooling, a secondary oil-containment pit, and separation/compartmentation are applied. If the cooling tower has flammable fill/body material it is protected with sprinklers. Early detection and appropriate suppression (clean agent/water-based) are planned for cable galleries and the control room.
Why is gas detection so critical in a geothermal plant?+
Because both of JES's main special risks involve invisible gases: toxic/flammable H2S and — in binary plants — flammable organic-fluid vapour. Both can accumulate unseen; moreover, H2S dulls the sense of smell at high concentrations, so 'no smell' does not mean safe. Fixed and portable gas detection is therefore at the heart of JES fire/life-safety design: an early alarm enables both evacuation and measures against flammable accumulation (increasing ventilation, stopping equipment). Detection works integrated with the facility control/SCADA system.
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