Gas Detection System Design and Compliance in Thailand

The scope of the gas detection work we deliver

The first question most buyers ask is “which gas detector model should we use?” — a question that cannot be answered yet, because the right model depends on the gases actually present on site, the nature of the leak, the contaminants in the atmosphere, the hazardous area classification, and the control system the plant already has. This page is about selection, design, and getting the system through acceptance under Thai law. If you are looking for model-level information and product specifications, see the Consilium Safety page.

Refineries in Thailand, oil and LPG depots in the eastern region, petrochemical plants and ports do not need a single “gas leak detector”. They need a gas detection system that answers four questions in full: where the gas will leak from, whether that gas rises or sinks, which sensing technology is needed to “see” the actual gas, and what the system has to command once the alarm sounds.

The work SATU Innovative designs, supplies, installs, commissions and maintains in Thailand covers:

• Fixed gas detection system — detector heads for flammable gas, toxic gas and volatile organic compounds (VOCs), with controllers, alarm logic and interfacing to the plant’s existing control system.
• Portable gas detectors — entry into confined spaces, work requiring a hot work permit, and leak surveys along pipe runs and at flanges.
• Flame detection system — for outdoor hazardous areas and process areas, where a release may ignite before the gas cloud reaches a gas detector head.
• Fire and Gas (F&G) system — bringing gas and flame detection signals together into a single system, with a Cause and Effect (C&E) matrix and interfacing to a PLC or DCS.
• Linear heat detection (LHD) — for long runs where a fire can start at any point along the length, such as conveyors, cable trays and pipe runs. See fibre-optic linear heat detection for details.

The equipment we build these systems around is the ST family from Consilium Safety, which has detector heads for flammable gas, toxic gas, volatile organic compounds and duct applications, with matching controllers. The flame detection equipment is from Micropack. For the model list, certification information and full specifications, see the Consilium Safety page, and for an overview of everything we do, see our services.

Names that do not match: what the law, the TOR and the engineers call this equipment

The first obstacle on this work is not technical but linguistic. Each document calls the same group of equipment by a different word, and the inspector reads the words in the statute, not the words an engineer types into a search box. Writing your Terms of Reference (TOR) in the words used by the law that applies to your establishment therefore removes far more argument at the acceptance inspection than writing it in the words that come naturally.

All of these mean the same group of equipment. A note on spelling: every Ministerial Regulation cited on this page uses the Thai word “ก๊าซ”, while “แก๊ส” is the form in general spoken use and in product names. Both are correct, but in specification documents and TORs use “ก๊าซ”, to match the text the inspector is holding.

This is not a question of style; it has real consequences on the day of inspection. A system that works perfectly well, but whose specification is written in words that do not match the Ministerial Regulation governing that establishment, is often questioned as being a different kind of equipment from the one the law requires — and then time is lost explaining after the fact.

Fixed gas detection system

A fixed gas detection system has three layers that must be designed to work together. The first layer is the detector heads and transmitters out in the hazardous area. The second is the field cabling and the controller that takes the readings in. The third is what the system makes happen once a reading reaches an alarm level, whether that is field sirens and beacons, an alarm signal into the control room, a shutdown command, or logging the event as evidence. Specify only the first layer and leave the other two out, and what you get is a detector head that makes a noise, not a safety system.

The third layer is the one most TORs write most thinly, and the one the law cares about most, because the requirements in the fuel-sector Ministerial Regulations (กฎกระทรวง) all say the same thing: the equipment must be “in serviceable condition and switched on at all times”, which is a continuing duty, not a condition that applies only on the day of installation.

Retrofit to an existing control system

Most work in Thailand is an upgrade to an existing system rather than a new build, so what decides whether a job is actually workable is the interface. The ST650EX, for example, provides a 4–20 mA output and has self-diagnostics, so it can be connected to the control system the site already has — the existing control panel, PLC or DCS — without replacing the whole control system. Signal format and self-diagnostic functions differ between models in the family; please confirm against the product data for the model actually to be used before specifying the interface. For the full model list, see the Consilium Safety page.

What has to be settled clearly at the outset is not the number of detector heads, but the alarm logic, the voting arrangement required before a shutdown is commanded, and where the system will log events. Those three can be agreed on paper in a day; left until commissioning, they become rework that costs money.

Portable gas detectors

Portable instruments are used for confined-space entry, for work carried out under a hot work permit, and for leak surveys. We supply portable instruments in both multi-gas and single-gas types, and the number of gases measured and the sensor types differ from model to model; please ask our engineering team on the basis of the actual work. Work in confined spaces under Thai law requires at least oxygen and flammable gas to be evaluated, so choosing an instrument on a channel count that has been misunderstood becomes a compliance problem, not merely a specification problem.

One point has to be understood on both sides: a portable instrument is not a substitute for a fixed system, because a portable instrument measures only while somebody is standing there holding it, whereas a fixed system watches continuously, even when nobody is in the area. The two answer different questions, and the law imposes them in different contexts.

Choose the sensor technology to match the gas you actually have: CAT / NDIR / TCD / MPS

The most dangerous failure of a gas detection system is not a false alarm but silence. A catalytic sensor that has been degraded by poisoning still reads zero as normal, and still passes its self-test every time. The screen in the control room therefore looks exactly as it does on a day when everything is fine. Choosing the wrong technology does not make the system alarm wrongly; it makes the system not alarm at all. And on a control panel, silence and safety look precisely the same.

The question that decides whether a system will actually work is therefore not the brand and not the price, but “what gas do you actually have, and which sensor technology can see it?” Each type of sensor relies on a different physical principle, so each has a different blind spot.

• Catalytic bead (CAT) — used for common flammable gases, reporting in %LEL. It works by combustion at the sensor surface, so oxygen must be present in the atmosphere for it to read at all, and it is at risk of permanent degradation from sensor poisoning, particularly by silicone compounds, sulphur, lead and chlorinated compounds — found in lubricants, coatings and cleaning agents, and in vapours from certain process operations. The damage is irreversible and gives no outward sign.
• Infrared (NDIR) — measures infrared absorption by the gas molecule, so sensor poisoning does not arise, it does not degrade after exposure to high concentrations, and it still works in low-oxygen atmospheres. It suits hydrocarbons. The real weakness of NDIR is not chemistry but optics: a dirty, wetted or obstructed lens will reduce performance, and there are groups of gases NDIR cannot see at all.
• Thermal conductivity (TCD) — relies on the difference between the thermal conductivity of the target gas and that of air, so it suits gases whose thermal conductivity differs markedly from that of air, and it depends on neither oxygen nor infrared absorption. It is therefore the answer on jobs where both the combustion principle and the infrared principle fail.
• Molecular Property Spectrometer (MPS) — another sensor type the ST650EX supports as an option. Confirm the supported gas list and per-gas performance against the latest product data before writing it into a specification, rather than relying on marketing literature.

The ST650EX uses replaceable sensors, with a choice of CAT, infrared (NDIR), TCD and MPS types. In practice this means that when a sensor degrades or reaches the end of its life, what has to be changed is the sensor, not the whole field device — a materially different figure over the whole life of the system.

Hydrogen: the blind spot every Thai-language page names and none offers a way out of

Every source agrees that infrared sensors cannot detect hydrogen, and stops the sentence there. The physical reason is that hydrogen is a homonuclear diatomic molecule, so bond vibration produces no change in dipole moment; with no change in dipole moment, the molecule does not absorb infrared light. An NDIR device is therefore not “reading it wrong”: it cannot see hydrogen at all, and it still passes its self-test as normal while the gas accumulates.

There are three options that actually work, and all three are sensors supported on the same model of device: CAT (accepting the conditions that oxygen must be present and that there is a sensor poisoning risk) and TCD (which suits hydrogen, because the thermal conductivity of hydrogen differs greatly from that of air), with MPS as a third option whose per-gas performance must first be confirmed against the product documentation.

This is no longer a hypothetical case in Thailand. Hydrogen turns up in three places that are usually specified from a generic hydrocarbon template: forklift and materials-handling battery charging rooms in warehouses, battery energy storage systems (BESS) now being installed both inside factories and on the power generation side, and hydrogen-bearing process units in refineries. In all three, using infrared sensors from the old template gives a system that looks complete on the drawing and does not work in practice.

%LEL, ppm and %Vol: three units, three questions — not three settings on the same instrument

%LEL is used for flammable gas, measured against the lowest concentration at which the substance will ignite or explode (Lower Explosive Limit, LEL); it is a unit of explosion risk. ppm is used for toxic gas, which is harmful to health at concentrations so low that the flammable range has not been reached. %Vol is used for proportion by volume, e.g. oxygen. Using an instrument that reports in %LEL to watch for a toxic gas is therefore the same as monitoring nothing at all.

The clearest example in Thailand is ammonia in cold stores and food processing plants, which is both toxic and flammable. The machinery room therefore needs both an alarm in ppm to protect people and an alarm in %LEL to protect the building. The two answer different questions and command different actions, so they are different detector heads — not two settings on the same instrument.

Five questions to answer before finalising a specification

These are the five questions we put back to a client every time, before we quote, and the first four settle almost the whole choice of sensor type before any brand is discussed.

1. Target gases and the reporting unit — the actual list of gases present in the area, the values to be monitored, and whether reporting is in %LEL, ppm or %Vol.
2. The nature of the leak — slow seepage at flanges and seals, or a high-pressure jet release. The two cases put detector heads in completely different places.
3. Contaminants in the area — are silicone compounds, sulphur, lead or chlorinated compounds present? This is what decides whether a CAT sensor can be used at all — and whether oxygen is certain to be present at all times.
4. Hazardous area classification and certification bodies — how the area is classified, and whose certificates the applicable Ministerial Regulation (กฎกระทรวง) accepts.
5. Access for maintenance — are the detector heads in pits, beneath platforms or at height, and what permits have to be obtained every time someone goes in to calibrate them?

The first four choose the technology; the fifth sets the whole-life cost, which on many projects exceeds the initial purchase price and is the item most often left unassessed until the year-three maintenance budget.

Flame detection and Fire and Gas (F&G) systems

A gas detection system works when gas drifts as far as a detector head. But in tank farms, at jetties and in open-air process areas, the wind may dilute the gas cloud before it reaches a head, or the leak may ignite at the point of release, leaving no cloud to detect in the first place. High-risk areas therefore need two layers — a gas detection layer and a flame detection layer — working together under a single Cause and Effect (C&E) matrix.

The flame detection equipment in the systems we deliver is made by Micropack, which Consilium Safety acquired in 2016 and which handles flame detection for the group. That is why flame detection products do not appear in the industrial gas detection catalogue. Buyers are often confused when they open the gas catalogue, find no flame detectors in it, and wrongly conclude that this manufacturer does not offer them. Models, certification details and detection ranges for Micropack equipment are on the Consilium Safety page.

False alarms: a legal compliance problem, not just a nuisance

The causes of false alarms in Thai plants are almost entirely predictable in advance: welding and spark-producing work carried out under permit, sunlight reflected off metal and water surfaces, heat from hot surfaces in the process, and a flare in the detector’s line of sight.

The consequence is what turns this into a legal matter. When a false alarm stops production, what invariably happens is that someone inhibits or mutes that device — and a device that has been disabled cannot comply with the requirement to be “in serviceable condition and switched on at all times”, however complete the detector-head layout on the drawing may look. False-alarm immunity is therefore not a marketing feature but the condition that keeps the system legally compliant a year after handover.

Decision logic and voting arrangements

At F&G system level, what has to be designed is not just the number of devices but the decision logic: how the first-stage alarm (Alarm Low) differs from the high alarm (Alarm High); how many devices must signal before a shutdown is commanded (the voting arrangement, e.g. 1oo2 or 2oo3); which signals raise an alarm only and which command emergency shutdown (ESD); and where the readings are recorded.

The voting arrangement balances two risks that pull against each other: the risk of failing to detect a real event, and the risk of stopping production unnecessarily. 1oo2 favours certainty of detection; 2oo3 is the compromise that tolerates one faulty device without tripping the plant. Settling this clearly at the outset is what keeps the system from being permanently muted six months into service.

A caution about SIL: SIL is a property of the safety loop as a whole, from the detection device through the logic solver to the final element — not a badge stuck on a single box. An individual device can therefore only be described as “SIL 2 capable”. A TOR stating that “the device must be SIL 2” without defining the boundary of the loop is a requirement that cannot be demonstrated in practice.

When Thai law requires a gas detection system

The straightforward answer is that Thai law does not require every factory to install a gas detection system, but it does require one explicitly in specific situations. What follows are the cases in which the law names this class of equipment directly, with citations that can be checked against the Royal Gazette.

1. Movable liquefied-gas cylinders stored inside a building

The Ministerial Regulation prescribing standards for the administration, management and conduct of occupational safety, health and working environment in relation to fire prevention and suppression, B.E. 2555 (2012) (กฎกระทรวง กำหนดมาตรฐานในการบริหาร จัดการ และดำเนินการด้านความปลอดภัย อาชีวอนามัย และสภาพแวดล้อมในการทำงานเกี่ยวกับการป้องกันและระงับอัคคีภัย พ.ศ. 2555) (Royal Gazette, Vol. 130, Part 2 Ko, 9 January 2013), Clause 20(2), provides that where gas cylinders are stored inside a building they must be stored separately in a room with walls of fire-resistant material, with good ventilation or air exchange, and with an automatic gas detection system (ระบบตรวจจับก๊าซอัตโนมัติ), stored together in quantities of not more than 2,000 litres per location, with each location not less than 20 metres from the next.

Two points to note. First, the whole of Clause 20 deals with “the storage of movable liquefied-gas cylinders” (ถังก๊าซชนิดเคลื่อนย้ายได้ชนิดของเหลว), so it does not automatically cover every type of gas cylinder. Second, this is occupational safety and health law, so it applies to every employer, not only to factories licensed under the factory law — which makes it the widest-reaching of all the requirements on this page.

2. Work in confined spaces (ที่อับอากาศ)

The Ministerial Regulation on confined spaces, B.E. 2562 (2019) (กฎกระทรวงฯ เกี่ยวกับที่อับอากาศ พ.ศ. 2562) (Vol. 136, Part 18 Ko, 15 February 2019), Clause 6, requires the employer to arrange for measurement, recording of the measurement results, and evaluation of the atmospheric condition before employees enter to work and while the work is in progress. Clause 1 defines a “hazardous atmosphere” (บรรยากาศอันตราย) to include oxygen below 19.5 per cent or above 23.5 per cent by volume; gas, vapour or mist capable of igniting or exploding, in excess of 10 per cent of the lowest concentration in air of each chemical at which it may ignite or explode (lower explosive limit); and combustible or explosible dust at or above its minimum concentration. The records of the results must be kept at the establishment for at least 1 year.

3. Liquefied petroleum gas (LPG) establishments

Several Ministerial Regulations on the LPG side require an “LPG leak audible alarm device (เครื่องส่งเสียงดังเมื่อก๊าซปิโตรเลียมเหลวรั่ว)” to be installed, and the minimum number and the areas in which they must be installed differ from one Ministerial Regulation to the next. This table is what the person writing the TOR has to look at before anything else, because it fixes both the minimum quantity and the positions.

Every one of the regulations above imposes the same continuing duty: the equipment must be checked to ensure it is in serviceable condition and switched on at all times. But none of them sets a testing frequency.

4. Natural gas service stations (NGV/CNG)

The Ministerial Regulation on natural gas service stations (กฎกระทรวง สถานีบริการก๊าซธรรมชาติ), B.E. 2564 (2021) (Vol. 138, Part 77 Ko, 23 November 2021), Clause 38, sets the number of gas leak audible alarm devices area by area: at least 1 unit each in the storage and dispensing tank room and in the compressor room; at least 1 unit per area in the compressor area; at least 2 units in the liquefied natural gas (LNG) storage area (บริเวณพื้นที่กักเก็บก๊าซธรรมชาติเหลว); and at least 1 unit at the pressure regulating and metering station. Clause 39 requires at least 2 fire detection devices (เครื่องตรวจจับการเกิดไฟ) in the LNG storage area, and Clause 40 provides that both groups of equipment must comply with Thai Industrial Standards (มาตรฐานผลิตภัณฑ์อุตสาหกรรม), NFPA 72, or another standard notified by the Minister, must be in serviceable condition and switched on at all times, and must be tested and inspected at least once a year.

Clause 40 matters more than its own subject matter, because it is the point at which Thai law names an international standard directly in the text of the statute. It is therefore the clearest evidence that NFPA is a citable compliance route, not merely a vendor claim.

What Thai law does “not” require, and what gets cited wrongly

• The Ministry of Industry Notification on Fire Prevention and Suppression in Factories, B.E. 2552 (2009) (ประกาศกระทรวงอุตสาหกรรม เรื่อง การป้องกันและระงับอัคคีภัยในโรงงาน พ.ศ. 2552) (Vol. 126, Special Part 143 Ngo, 30 September 2009) mandates a fire alarm system, which Clause 3 defines to include smoke, heat or flame detectors operating automatically. Clause 4 requires it to be automatic in areas that have no permanently assigned workers and in which electrical equipment is installed or in use, or flammable materials are stored, and Clause 5 requires installation in accordance with “accepted international standards”. This Notification mandates fire detection; it does not require every factory to install a gas detection system.
• The Ministerial Regulation on hazardous chemicals, B.E. 2556 (2013) (กฎกระทรวงฯ สารเคมีอันตราย พ.ศ. 2556), Clause 29 is a duty to measure and analyse the concentration of hazardous chemicals in the workplace atmosphere and to report the results to the Director-General within 15 days of the day the results become known, which is normally done by taking samples and analysing them in a laboratory. It is not a requirement to install fixed gas detector heads. This clause is cited very often in purchase requisitions, and citing it that way is a misuse.
• A TIS standard specific to gas detectors — “Thai Industrial Standards (มาตรฐานผลิตภัณฑ์อุตสาหกรรม)” is referred to as an acceptable class of standards in the LPG and NGV Ministerial Regulations, but as far as could be verified, no TIS standard issued specifically for gas detectors has yet been found. If a bidder claims one exists, ask for the TIS number to confirm it.

The commonest pitfall in Thai specifications is taking the 10%-of-LEL figure and writing it in as the alarm set point for a fixed system. That figure is the definition of a hazardous atmosphere for work in confined spaces, not an alarm set point the law requires a fixed system to use. The same goes for the 19.5–23.5 per cent oxygen band: it is a definition, not a device setting. As far as could be verified, Thai law sets no alarm set point at all for fixed gas detection systems.

For a detailed treatment of each Ministerial Regulation and how to cite them in procurement documents, see the regulatory article series at Industry Insights.

Hazardous area equipment certification, detector location and the number of detector heads

The words ATEX and IECEx appear nowhere in Thai law. What the law does set out is hazardous area classification and a list of certification bodies. The Ministerial Regulation on Electrical Systems and Lightning Protection Systems of Oil Business Establishments, B.E. 2556 (2013) (กฎกระทรวง ระบบไฟฟ้าและระบบป้องกันอันตรายจากฟ้าผ่าของสถานที่ประกอบกิจการน้ำมัน พ.ศ. 2556) (Royal Gazette, Vol. 130, Part 29 Ko, 27 March 2013) classifies areas, in Clause 9, into “Hazardous Area Type 1” (บริเวณอันตรายแบบที่ 1) and “Type 2” (แบบที่ 2), and Clause 16 states that apparatus, electrical appliances and equipment accepted for use in those areas must be certified by a body falling within one of the nine entries listed in that clause: the Thai Industrial Standards Institute (TISI, สมอ.), UL, EECS, PTB, LCIE, CESI, CSA, TIIS, or another organisation approved by the Department of Energy Business (DoEB).

The reason certificates from Europe are accepted lies in this list itself. PTB (Germany), LCIE (France), CESI (Italy) and EECS (the United Kingdom) are European certification bodies that issue certificates by the ATEX route. Equipment therefore qualifies because the body issuing the certificate is named in Clause 16, not because a mark is printed on the housing. When comparing bidders, you should therefore ask for the certificate itself, with the name of the certification body and the certificate number, rather than accepting the words “ATEX certified” from a brochure alone.

The LPG regulations work to different criteria and have one further area type. The Ministerial Regulation on Electrical Systems and Lightning Protection Systems of Liquefied Petroleum Gas Business Establishments, B.E. 2564 (2021) (กฎกระทรวง ระบบไฟฟ้าและระบบป้องกันอันตรายจากฟ้าผ่าของสถานที่ประกอบกิจการก๊าซปิโตรเลียมเหลว พ.ศ. 2564) (Royal Gazette, Vol. 138, Part 45 Ko, 12 July 2021) classifies areas, in Clause 9, into three types, adding “Hazardous Area Type 3” (บริเวณอันตรายแบบที่ 3). Clause 14 requires equipment used in Type 1 and Type 2 areas to be certified by TISI or another organisation approved by the DoEB. Clause 15 requires, for Type 3 areas, that equipment must have a fully sealed enclosure preventing electrical sparks or hot particles from passing outside it, together with requirements on the wiring method. This clause is hardly ever written up in the Thai-language material, and it is the clause that stops a specification copied from an oil-side project being used directly on LPG work.

Mounting height: how high above floor level

Mounting height is not a matter of convenient cable routing; it is set by the density of the gas relative to air, and in the case of LPG the law states the figure outright. The Department of Energy Business Notifications on Criteria and Methods for Installing LPG Leak Audible Alarm Devices (ประกาศกรมธุรกิจพลังงาน เรื่อง หลักเกณฑ์และวิธีการติดตั้งเครื่องส่งเสียงดังเมื่อก๊าซปิโตรเลียมเหลวรั่ว) are issued as separate editions by type of establishment: the editions for filling rooms, B.E. 2564 (2021) and storage buildings, B.E. 2564 (2021) (both Royal Gazette, Vol. 138, Special Part 289 Ngo, 24 November 2021), the edition for premises of use, Category 3 (สถานที่ใช้ ลักษณะที่สาม), B.E. 2564 (2021) (Vol. 138, Special Part 321 Ngo, 31 December 2021), and the edition for filling plants, B.E. 2565 (2022). All of them use the same technical wording in Clause 2:

• The gas leak audible alarm device must be of a type for use in hazardous areas specifically for liquefied petroleum gas, in accordance with the Ministerial Regulation on electrical systems for liquefied petroleum gas business establishments.
• Installation must comply with the Thai Electrical Installation Standard of the Engineering Institute of Thailand under H.M. the King’s Patronage (EIT), and must be approved by the Department of Energy Business.
• The LPG leak quantity measuring device (อุปกรณ์วัดปริมาณก๊าซปิโตรเลียมเหลวรั่ว) must be installed no more than 30 centimetres above floor level, because LPG is heavier than air and flows down to low points.
• The installation must be able to give a perceptible alarm indication when there is a gas leak.

Clause 3 of this set of Notifications fixes the position as well: near the centre of the storage and dispensing tank group, covering the pump group and the tanker unloading connection, and near the centre of the cooking cylinder group. For storage buildings it adds that one device is to be installed per group, for groups of cylinders or canisters not exceeding 2,400 litres in each group. Note that the 2,000-litre figure in the legal section above and the 2,400 litres here come from different laws and different contexts. The first is occupational safety and health law on storing cylinders inside a building; the second is fuel law on the number of devices per cylinder group in a storage building. The two figures do not conflict.

Conversely, ammonia in cold stores and food processing plants is lighter than air, so detector heads have to be high up, near the ceiling. Using one height across a whole site is a mistake that goes unnoticed until there is a real incident. And the requirement above for approval by the Department of Energy Business is the point at which equipment that has already been purchased runs into trouble on the day of inspection, not the day of installation.

Number of detector heads: how many points

For process areas, where Thai law sets no number of heads, the method used internationally is detection coverage mapping, which starts by defining the possible leak scenarios, the prevailing wind direction and the geometry of obstructions, and then demonstrates what percentage of the target volume the proposed set of detector heads actually covers.

The guidance that can be cited is BS 60080:2020, on hazard detection mapping and the location of fixed flame and gas detectors, which sets out three approaches: prescriptive, volumetric and scenario-based. This document is a BSI standard and engineering good practice, not a Thai legal requirement, but it is the document that makes the answer on the number of detector heads demonstrable rather than an estimate (please do not write “IEC 60080”, which is a different standard and has been withdrawn).

For mapping work of this kind, Micropack has Hazmap3D, software built specifically for F&G consultancy work, which makes the output a traceable document rather than a detector layout drawn from experience.

A detection coverage mapping report that is usable in practice must state at least four things: the leak scenarios assumed, the wind directions considered, the percentage of volume or of scenarios detected against the agreed criteria, and the list of points that still cannot be detected together with the reasons. The last of these is what separates a real report from a sales drawing, and it is what changes the explanation on the day of inspection from “installed as the supplier proposed” to “installed in line with the results of a study whose method is stated”.

Installation, testing, calibration and the documents an inspector actually asks to see

On calibration intervals it is better to speak plainly, and this page will not invent a figure. Thai law states a clear test interval for gas detection equipment in one case only: the Ministerial Regulation on natural gas service stations (กฎกระทรวง สถานีบริการก๊าซธรรมชาติ), B.E. 2564 (2021), Clause 40, which requires testing and inspection at least once a year.

There is a pair of clauses that are often cited the wrong way round and should be put right. The Ministerial Regulation on LPG depots (กฎกระทรวง คลังก๊าซปิโตรเลียมเหลว), B.E. 2564 (2021), Clause 39 requires the depot’s alarm system (ระบบสัญญาณเตือนภัย) to be tested at least once a year, which is a different item from Clause 40, which deals with the LPG leak audible alarm device (เครื่องส่งเสียงดังเมื่อก๊าซปิโตรเลียมเหลวรั่ว) — and Clause 40 does not state a test interval. Anyone citing Clause 39 as the calibration interval for gas detector heads is citing a clause that does not match the equipment.

Under the LPG regulations, every one states only the continuing duty that the equipment be in serviceable condition and switched on at all times, without stating a frequency. So anyone who says “Thai law requires calibration every three months” or “every six months” is saying something that is not in the text. The documents that actually set the interval are the manufacturer’s manual, together with IEC/EN 60079-29-2 on the selection, installation, use and maintenance of flammable gas detection apparatus, which is the document that sets out methods and frequency of functional verification and the records to be retained.

The relevant parts of IEC 60079, and what each one governs

• IEC 60079-10-1 — hazardous area classification for gases and vapours
• IEC 60079-14 — design, selection and erection of electrical installations in explosive atmospheres
• IEC 60079-29-0 — general requirements for gas detection apparatus
• IEC 60079-29-1 — construction, performance and test methods for flammable gas detectors, portable, transportable and fixed
• IEC 60079-29-2 — selection, installation, use and maintenance, including methods and frequency of verification and the records to be retained

We write the maintenance plan to reference the manufacturer’s manual together with this set of documents, and we time it to fall in step with the statutory inspection cycles the site already has to carry out: documented fire safety inspection of the factory at least once a month (Ministry of Industry Notification (ประกาศกระทรวงอุตสาหกรรมฯ) B.E. 2552 (2009), Clause 26); inspection of the condition and readiness of portable fire extinguishers at intervals of not more than 6 months (the same Notification, Clause 7); and fire and evacuation drills at least once a year (Ministerial Regulation on fire prevention (กฎกระทรวงฯ อัคคีภัย) B.E. 2555 (2012)). A plan that moves with these cycles will defend itself on the day of inspection, instead of being a free-floating schedule nobody follows.

Bump test, calibration and functional test: three things that are not the same

• bump test — applying calibration gas to the detector head to confirm the sensor still responds and the alarm still operates. It answers the question “is it still alive?”, not “is it reading correctly?”
• calibration — adjusting the reading to match a known concentration. It answers the question “can the number be trusted?”
• functional test — testing the C&E matrix along the whole path, from the detector head, through the logic and the voting arrangement, to the final device that has to operate, such as a siren, a valve or a shutdown command. It answers the question “what does the system actually do when it happens for real?”

Many service contracts roll all three into a single line reading “annual calibration service”. The result is a document that cannot prove whether the command path was ever tested — the one thing that has any meaning on the day something happens. All three should be stated separately in the TOR, together with who keeps the records.

Maintenance access is a cost that recurs every cycle

What makes maintenance plans fail in Thailand is not the frequency but access to the installed position. A gas detector head placed, on sound engineering grounds, in a pit or beneath a platform is a point that requires a confined-space entry permit every time it is calibrated. In that situation, the ability of the ST650EX to separate the sensor from the transmitter by cable runs of up to 150 metres allows the sensor to sit where the gas actually accumulates, while the transmitter and its display sit where a technician can reach them.

Flame detectors mounted at height, for their part, can be function-tested from a distance with the FS301 remote flame simulator. This is not just a question of scaffolding cost but of legal compliance, because if equipment mounted at height is never functionally tested, there is no evidence at all to prove that it is “in serviceable condition” as the law requires. Both points should be assessed when prices are being compared, not when the year-three maintenance budget is being drawn up.

What we deliver as documents

The work that makes a gas detection system function in practice happens before and after the equipment is delivered, and what the inspector asks to see is documents, not boxes. Our scope is therefore stated as countable deliverables.

• A detection coverage mapping report with the leak scenarios, wind direction, coverage criteria and a list of the points that still cannot be detected
• A selection justification document — why this sensor technology for this gas, why this number of heads, why this position and height. This is the document an inspector actually asks to see, and it is what a model-for-model quotation cannot give you.
• A Cause and Effect (C&E) matrix with the alarm levels, the voting arrangement and the ESD command path
• A compliance dossier for the acceptance inspection — equipment certificates with the name of the certification body and the certificate number, the approval documents required by law, the commissioning and Site Acceptance Test (SAT) results, and the maintenance plan with its record forms

What to state in the TOR or request for quotation

• The list of target gases, the values to be monitored, and the units to be reported (%LEL, ppm or %Vol)
• The hazardous area type, and the certification bodies that are acceptable under the Ministerial Regulation applying to your establishment
• The contaminants present in the area, such as silicone compounds, sulphur, lead and chlorinated compounds, which decide whether a CAT sensor can be used at all
• The mounting height dictated by the density of the gas, and the access route for maintenance
• The signals and interfaces to be connected to the existing system, including the alarm logic and the voting arrangement required before a shutdown is commanded
• The scope of commissioning and SAT, kept separate from bump test, calibration and functional test, with the party responsible for keeping the records identified
• The list of spare parts and spare sensors to be delivered with the system

The analysis work behind all of this is set out under safety engineering and risk assessment services.

Let us review your specification before you issue your TOR

We do not start by proposing an equipment model, because the right model depends on the gas, the area and the control system you already have. What is most useful to you is a specification review before the document goes out to the market, because after that, correcting it costs time and damages your relationship with bidders.

Send us the following four things and our engineering team will come back with comments on the specification, a system approach and a scope of work that can genuinely be priced, rather than a catalogue.

• The list of target gases and the values to be monitored, stating whether hydrogen or contaminants that destroy sensors are present in the area.
• The plot plan and the hazardous area classification drawing, if you have one, including the positions of tanks, pumps, loading and unloading points and the prevailing wind direction.
• The existing control system the detection has to connect to — the existing control panel, PLC or DCS — and the signal formats it supports.
• The type of establishment and the authority that regulates it, because these determine the certification requirements and the inspection cycle you have to comply with.

SATU Innovative supplies, designs, installs, commissions and maintains gas and flame detection systems for industrial work in Thailand, designed to fit the site’s overall fire protection system, and hands over documentation that can be used to demonstrate legal compliance at the acceptance inspection.

Contact the engineering team: send your project details through the contact form, or call 062 469 4617 (+66 62 469 4617), or email solutions@satu-innovative.com.

Frequently asked questions

What is the difference between a gas leak detection system and a gas leak detector?

In practice, a “gas leak detector” usually means a single device, while a “gas leak detection system” means detector heads at several points, field cabling, controllers, alarm logic and what the system commands to happen when the alarm sounds. Factory and fuel depot work needs the latter, because detecting gas with no command logic behind it does not actually reduce the risk. A note on spelling: every Ministerial Regulation uses the word “ก๊าซ”, while “แก๊ส” is the everyday spoken form. Both are correct, but in a specification document the wording should match that of the statute.

Does our factory have to install a gas detection system under Thai law?

Not every factory. Thai law requires it only in particular cases. For example, storing movable liquefied-gas cylinders (ถังก๊าซชนิดเคลื่อนย้ายได้ชนิดของเหลว) inside a building requires an automatic gas detection system (ระบบตรวจจับก๊าซอัตโนมัติ) under the Ministerial Regulation (กฎกระทรวง) on fire prevention and suppression, B.E. 2555 (2012), Clause 20(2). Several types of LPG establishment — LPG depots, filling plants, filling rooms, storage buildings, service stations, premises of use and retail shops among them — are required to have an LPG leak audible alarm device (เครื่องส่งเสียงดังเมื่อก๊าซปิโตรเลียมเหลวรั่ว), with the minimum number of units and the areas in which they must be installed differing from one Ministerial Regulation to the next. Natural gas service stations have requirements under the Ministerial Regulation (กฎกระทรวง สถานีบริการก๊าซธรรมชาติ) B.E. 2564 (2021), Clauses 38–40. Ordinary factories that do not fall into these categories usually install detection on the basis of a risk assessment, not because of a direct legal requirement.

What is the difference between catalytic bead (CAT) and infrared (NDIR) sensors, and which should be chosen?

CAT works by combustion at the sensor surface, so it needs oxygen in the atmosphere and is at risk of permanent degradation from sensor poisoning, in particular by silicone compounds, sulphur, lead and chlorinated compounds. NDIR measures infrared absorption, so sensor poisoning does not arise, it does not degrade after exposure to high concentrations, and it works even where oxygen is low. The weak points of NDIR are a lens that is dirty, wetted or obstructed, and the fact that there are groups of gases NDIR cannot see at all. The choice therefore has to start from the actual list of gases and the contaminants present in the area, not from the price per point.

Our existing system uses infrared (NDIR) sensors — will it detect hydrogen?

No, and the reason lies in the physics of the molecule. Hydrogen is a homonuclear diatomic molecule, so bond vibration produces no change in dipole moment. With no change in dipole moment there is no infrared absorption. An NDIR device is therefore not reading the value wrongly — it cannot see hydrogen at all, and it still passes its self-test as normal while the gas accumulates. The workable options are CAT (accepting the conditions around oxygen and sensor poisoning), TCD (well suited to hydrogen, because its thermal conductivity differs greatly from that of air), and MPS as a third option, for which per-gas performance should be confirmed against the product data first. The cases seen most often in Thailand are forklift battery charging rooms, BESS installations and hydrogen-bearing process units, which are commonly specified from a generic hydrocarbon template.

What is the difference between %LEL and ppm, and which figure should be watched?

%LEL is used for flammable gas, measured against the lowest concentration at which the substance will ignite or explode (Lower Explosive Limit); it is a unit of explosion risk. ppm is used for toxic gas, which is harmful to health at concentrations so low that the flammable range has not been reached. One area may have to be monitored in both units at once — ammonia in a cold store, for example, is both toxic and flammable, so the machinery room needs a ppm alarm to protect people and a %LEL alarm to protect the building. The two figures answer different questions and command different actions, so they are different types of detector head, not two settings on the same unit.

How often does a gas detector have to be calibrated, and how does a bump test differ from calibration?

A bump test means applying calibration gas to confirm that the sensor still responds and the alarm still operates. Calibration means adjusting the reading to match a known concentration. A functional test means testing the Cause and Effect matrix along the whole path through to the final device. The three are not the same thing and should be stated separately in the service contract. On frequency, Thai law states a clear interval in only one case: natural gas service stations, which must be tested and inspected at least once a year under the Ministerial Regulation (กฎกระทรวง สถานีบริการก๊าซธรรมชาติ) B.E. 2564 (2021), Clause 40. In other cases the law requires only that the equipment be in serviceable condition and switched on at all times. The documents that actually set the interval are therefore the manufacturer’s manual together with IEC/EN 60079-29-2.

How high above floor level do detector heads have to be mounted, and how many points are needed?

Mounting height is determined by the density of the gas. For LPG, the Department of Energy Business Notification (ประกาศกรมธุรกิจพลังงาน) on Criteria and Methods for Installing LPG Leak Audible Alarm Devices (issued as separate editions for each type of establishment), Clause 2, states that the LPG leak quantity measuring device (อุปกรณ์วัดปริมาณก๊าซปิโตรเลียมเหลวรั่ว) must be installed no more than 30 centimetres above floor level, because the gas is heavier than air. Gases lighter than air — ammonia in a cold store, for example — have to be mounted high, close to the ceiling. On the number of points, Thai law sets a minimum only for certain establishments; for the rest, the answer comes from detection coverage mapping following BS 60080:2020, which is a BSI standard and engineering good practice, not a Thai legal requirement, but which makes the answer on the number of heads demonstrable.

Does the equipment have to have ATEX or IECEx, and does Thai law accept it?

Thai law does not use the words ATEX or IECEx. What it does set out is hazardous area classification and a list of acceptable certification bodies. Under the Ministerial Regulation on electrical systems for oil business establishments (กฎกระทรวง ระบบไฟฟ้าฯ ของสถานที่ประกอบกิจการน้ำมัน), B.E. 2556 (2013), Clause 16, these are the Thai Industrial Standards Institute (TISI, สมอ.), UL, EECS, PTB, LCIE, CESI, CSA, TIIS, or another organisation approved by the Department of Energy Business (DoEB). On the LPG side, the Ministerial Regulation on electrical systems for liquefied petroleum gas business establishments (กฎกระทรวง ระบบไฟฟ้าฯ ของสถานที่ประกอบกิจการก๊าซปิโตรเลียมเหลว), B.E. 2564 (2021), Clause 14, requires certification by TISI or a body approved by the DoEB. The important point is that PTB, LCIE, CESI and EECS are European certification bodies that issue certificates by the ATEX route, so equipment qualifies because the body issuing the certificate is named in the list, not because a mark is printed on the housing. Ask for the certificate itself, with the name of the certification body and the certificate number.

Should the gas detection system and the factory’s existing fire alarm system be separate, or combined into one system?

In law they are separate systems, but they should work together under a single Cause and Effect matrix. The fire alarm system is governed by the Ministry of Industry Notification (ประกาศกระทรวงอุตสาหกรรม) B.E. 2552 (2009), which defines it as including smoke, heat or flame detectors operating automatically. The gas detection system is governed by a different piece of legislation and uses different terminology. In practice we usually keep both sets of logic in the same C&E matrix and have the gas detection system send status signals into the fire alarm system, so that the control room sees one picture. What has to be watched is not merging them so far that it is no longer clear which device sits under which law, because the certification requirements, the reference standards and the inspection cycles of the two systems are not the same.

Who has to approve the gas detection system design, and which authority do the documents go to?

It depends which law your establishment falls under. For LPG establishments, the Department of Energy Business Notification on the installation of LPG leak audible alarm devices, Clause 2(2), states plainly that the installation must follow the Thai Electrical Installation Standard of the Engineering Institute of Thailand and must be approved by the Department of Energy Business. For establishments under the factory law, inspection is a matter for the competent official under the factory law, while requirements on the occupational safety and health law side sit with the safety inspector of the Department of Labour Protection and Welfare. The common mistake is to finish procuring the equipment and only then find that it does not meet the approval conditions — a problem that arises on the day of inspection, not the day of installation.

Can a new gas detection system be connected to the factory’s existing control system?

In most cases, yes. Industrial gas detectors generally provide a 4–20 mA output, which connects to the existing control panel, PLC or DCS without having to replace the whole control system. Signal formats differ from model to model, however, so confirm against the product data for the model actually to be used before specifying the interface. What has to be agreed clearly from the outset is not the signal figure but the alarm logic, the low and high alarm levels, the voting arrangement before a shutdown is commanded, and where the system will log events.