Refrigerant Leak Detection ASHRAE 15 / EN 378 / ISO 5149 — Choosing Gas Detectors for Factories and Machinery Rooms in Thailand

A "leaking" refrigerant isn't just about lost cooling capacity and rising electricity bills — it's a matter of safety and legal compliance. Some refrigerants cause oxygen depletion (asphyxiation), some are toxic (e.g. ammonia), and many modern refrigerants (R-32, R-454B, R-1234yf) are flammable if they accumulate in an enclosed space.

That is why the international standards ASHRAE 15, EN 378, and ISO 5149 require refrigeration systems with charge above a threshold to have a refrigerant leak detection system that alarms and automatically activates ventilation. This article explains the standards, setpoints, sensor types, and how to choose the right system for projects in Thailand.

1. Why Detect Refrigerant Leaks — Three Invisible Hazards

Most HFC/HFO refrigerants are odorless, invisible, and heavier than air — a worker can lose consciousness before realizing it. This is why continuous fixed detection matters more than portable tools.

2. The Three Core Standards

ASHRAE 15 (Safety Standard for Refrigeration Systems)

The American standard, most-referenced in Thai projects. It defines:

• RCL (Refrigerant Concentration Limit) — the maximum concentration acceptable in an occupied space
• Systems with charge exceeding the room's RCL → require a machinery room + refrigerant detector + mechanical ventilation
• The detector must trigger both an alarm and automatic ventilation
• Used together with ASHRAE 34, which classifies refrigerant safety (A1/A2L/A2/A3 + B1/B2L/B2/B3)

EN 378 (Europe) and ISO 5149 (International)

EN 378 and ISO 5149 are "siblings" with very similar content, split into four parts (Part 1-4: basic requirements / design-construction / installation site / operation-maintenance). Highlights:

• Define charge limits by occupancy category (a/b/c) and each refrigerant's practical limit
• Charge above the practical limit → a detector that alarms + activates ventilation is required
• Specify sensor placement "where refrigerant tends to accumulate"

In plain terms: all three standards say the same thing — if there is enough refrigerant in the system to be hazardous when it all leaks into a room, you must have detection + alarm + ventilation.

3. Alarm Thresholds — What Setpoint?

The setpoint principle differs by refrigerant safety group:

LFL (Lower Flammable Limit) = the lowest concentration at which a refrigerant can ignite. Setting the alarm at 25% LFL gives a 4× buffer before the dangerous level — the standard value used by both EN 378 and IEC 60335-2-40.

4. Sensor Types — Match to the Job

Simple selection rules:

• Permanent room monitoring → NDIR (accurate, selective, long life)
• Walking to find a leak → heated diode or ultrasonic
• Ammonia systems → multi-level electrochemical

5. Sensor Placement — Wrong Spot = Useless

Refrigerant density dictates placement:

• Heavier than air (most HFC/HFO + CO2): accumulates at the floor → mount the sensor near the floor (~0.3 m) and close to leak sources (compressor, fittings, valves)
• Ammonia (lighter than air): rises → mount near the ceiling
• Add sensors in pits/sumps/confined low areas where refrigerant may flow and pool
• Avoid mounting near doors/air vents that dilute the gas before it reaches the sensor

Mounting an HFC sensor on the ceiling while the refrigerant pools on the floor = no detection even during a real leak — the most common installation mistake.

6. A2L Refrigerants (R-32, R-454B) — New Rules to Know

Modern low-GWP refrigerants (R-32, R-454B, R-1234yf) are classified A2L = mildly flammable. The IEC 60335-2-40 (A2L edition) standard adds:

• Units with charge above the room-size threshold must have built-in leak detection
• On detecting a leak, mitigation measures are required — fan purge, circuit cutoff, or pump down — so concentration never reaches the LFL
• Installation must strictly follow the manufacturer's manual (clearances, minimum room size, pipe location)

See more on A2L safety in R-32 A2L — Safety and Handling Guide and replacement selection in HFO R-449A vs R-454B vs R-513A.

7. Calibration and Sensor Maintenance

An uncalibrated sensor may fail to alarm during a real leak:

• Calibrate on schedule — typically every 6-12 months (per manufacturer + project requirement)
• Bump test — confirm the sensor actually responds to gas (not just powered on)
• Sensor life — electrochemical ~2 years, NDIR much longer
• Keep calibration records as evidence — government/ISO audits often require them

8. How to Find a Leak (When the System Alarms or You Suspect One)

Beyond fixed sensors, locating a leak uses several methods together:

1. Electronic detector (heated diode) — sweep the probe along pipes/fittings
2. Soap bubble test — large leaks show bubbles
3. UV dye (fluorescent tracer) — inject into the system, scan with UV light for stained spots; good for small hard-to-find leaks
4. Nitrogen pressure test / standing vacuum — pressure/vacuum check before charging
5. Ultrasonic — listen for leaks in hard-to-reach areas

Never use a halide torch on flammable A2L/A3 refrigerants — it is a direct ignition source.

9. Thai Requirements + Government Projects (TOR)

• Hazardous Substance License (Wor. Or.) — all refrigerants are hazardous substances under the Hazardous Substance Act B.E. 2535; importers/sellers must hold the proper license
• EIT/DPT standards — large refrigeration projects reference ASHRAE 15 / EN 378
• Cold-room/hospital/server-room TORs typically require: gas detector + ventilation + warning signage + leak-response plan + calibration records
• Commonly requested refrigerant documents: AHRI 700 purity certificate + SDS + license

Summary Table — Match the Detection System to the Job

Frequently Asked Questions

Q: Do small systems (home/office AC) need a detector?

A: Generally no, if the charge is below the room's threshold per the standard. But new A2L units with high charge installed in small rooms may meet the manufacturer's threshold requiring built-in leak detection — follow the unit's manual.

Q: Can a single sensor cover all refrigerants?

A: A semiconductor sensor detects broadly but is not gas-selective (false alarms easy). NDIR and electrochemical must be matched to the refrigerant in use — when changing the system's refrigerant, verify the existing sensor still supports it.

Q: Must the detector be tied directly to automatic ventilation?

A: Yes — both ASHRAE 15 and EN 378 require a machinery-room detector to automatically activate ventilation at setpoint, not just sound an alarm. An alarm alone does not reduce refrigerant concentration.

Q: How is CO2 (R-744) leak detection handled?

A: CO2 is heavier than air and odorless — use a CO2-specific NDIR sensor mounted near the floor. The main hazard is oxygen depletion in confined spaces; set alarms per O2/CO2 safety limits (not LFL, since CO2 is non-flammable).

Q: Does Sahawatthanakit only sell refrigerant, or also help with leak-detection documentation?

A: We supply refrigerants across all groups (HCFC/HFC/HFO/Natural), AHRI 700 certified, with full licensing, SDS, and supporting documents for TOR work. For detection-system specs that meet the standards, we provide technical guidance to match refrigerant to the safety requirements.

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Sahawatthanakit supplies refrigerants across all groups — HCFC + HFC + HFO + Natural (R-744/R-290) — AHRI 700 (2019) certified with full hazardous-substance licensing and documentation for government and ASHRAE 15 / EN 378 compliance work.

• Phone: 02-096-2118
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