Ammonia (NH3) Gas Detection

With zero global warming potential and zero ozone depletion potential, ammonia is considered one of the most cost effective, energy efficient, natural refrigerants for industrial refrigeration. However, ammonia is classified as a B2L refrigerant under the ISO 817 classification scheme, meaning it has higher toxicity and lower flammability than other refrigerants.

Ammonia safety


Safety is paramount for ammonia refrigeration systems. Ammonia is corrosive and human exposure will result in a chemical type burn. As ammonia is extremely hygroscopic (rapidly absorbing moisture), it readily migrates to moist areas of the body such as eyes, nose, throat and lungs.

UK Health and Safety Executive EH40 regulations and the US National Institute for Occupational Safety and Health (NIOSH) specify safe long term exposure limits for ammonia gas as 25 parts per million (PPM) for an 8-hour time-weighted average (TWA) and short term exposure limit (STEL) of 35 PPM for a 15 minute period. In contrast, the United States Occupational Safety and Health Administration (OSHA) is 50 PPM averaged over an 8-hour TWA. Levels of 300 ppm are considered immediately dangerous to life and health. Exposure to liquid ammonia will result in frostbite since its temperature at atmospheric pressure is -28F. Fortunately, ammonia has a low odor threshold of around 20 PPM so most people will be able to seek safety at lower concentrations.


Ammonia is considered a flammable hazard between concentrations of approximately 15% to 28% by volume in air. EN 378 stipulates that for flammable levels of ammonia, alarms should be set as follows:

  • At low alarm level 500 PPM (0.33% LEL) alarm and mechanical ventilation to be activated
  • At high alarm level 30,000 PPM (20% LEL) refrigerating system to be automatically stopped.

Guidance following the withdrawal of HSE’s PM81 publication, “Safe Management of ammonia refrigeration systems” for the food and drinks industries and other workplaces , states levels of 500 PPM for fan ventilation and alarm and a “practical” shut down level of 6.6% LEL or 10,000 PPM.

Ammonia Safety Compliance with Greenyard Frozen

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Ammonia hazard reduction and leak detection

The US environmental protection agency (EPA) outline situations where hazardous ammonia leaks are likely to occur:

  • Over pressure conditions and lifting of pressure relief valves
  • Seal leaks from rotating shafts and valve stems
  • Refrigerant piping failures due to loss of mechanical integrity from corrosion
  • Physical damage of system components from equipment collisions
  • Hydraulic shock
  • Hose failures that occur during ammonia deliveries

In addition to risks of personal injury, ammonia leaks have the potential of causing significant collateral damage including product loss due to ammonia contamination, interruption of refrigeration capacity, product loss due to refrigeration interruption, and potential for equipment and property damage resulting from the incident.

The refrigeration industry and governing organizations provide clear instructions to ensure that a properly designed, constructed, operated and maintained ammonia refrigeration system can be safely achieved. Two such requirements relative to leak detection are, “Maintain a leak-free ammonia refrigeration system. Investigate all reports of an ammonia odor and repair all leaks immediately” and “Consider installing ammonia detectors in areas where a substantial leak could occur if the facility is not manned 24 hours/day.”

Ammonia leak detection equipment

Bacharach provides innovative solutions designed for extreme temperature refrigeration environments, providing ammonia refrigerant safety compliance. Suitable for:

  • Mechanical rooms
  • Compressor rooms
  • Walk-in freezers & cold rooms,
  • Industrial cold storage
  • Chiller rooms

Two distinct technologies are available: the Multi Zone aspirated system and the MGS-400 and MGS-550 diffusion gas detection system. Both provide exceptional functionality and can be customized depending on your detection requirements and budget.

Ammonia leak detection locations

Although ammonia refrigeration plant locations in a typical room may have small leaks, these may be significant enough to cause a toxic hazard to personnel, and therefore sample locations/detectors should be located in the breathing zone (BZ), 1.5m from the ground, with an alarm level of 35 PPM. Typically, these same BZ sample locations/detectors will have the high alarm set at the 500 PPM level in accordance with EN378. However, locating the detectors intended for the 500 PPM alarm level may require a survey to be carried out as the BZ height may not always be applicable. Detecting this 500 PPM level is very difficult due to the nature of ammonia as it may simply rise past diffusion gas detectors. Typically, small leaks of ammonia rise and build up in the roof space of plant rooms at height. Therefore, the LEL sample points/detectors should be mounted within the roof space of the plant room to monitor for potentially hazardous levels of ammonia in the LEL range, and set to alarm at the appropriate levels. Mounting an LEL ammonia sample location/detector at lower level is not advisable. Typical mitigation to resolve ammonia build-up would be to vent the roof space and force exhaust of the roof space to atmosphere.

What system is right for you?

Deciding which system is right for you depends on several factors: total number of sampling areas, ammonia levels you want to detect, sampling frequency, integration with BMS/BAS control systems, maintenance requirements and CAPEX and associated OPEX cost.

Multi-Zone MGS-400 Series MGS-550
Multi-Zone MGS-400 Series MGS-550 Series
Integration with BMS / BAS control system Modbus, BACnet, LonWork and analog communications Modbus, Digital and analog communications Modbus, Digital and analog communications
Temperature Zone / Application Low and Medium Low and Medium Low and Medium
Sensing Medium Infrared Electrochemical (EC), Catalytic Bead (CAT) Electrochemical (EC), Catalytic Bead (CAT) or Semi Conductor (depending on PPM alarm range)
Sensor Typical Life Span Up to 7 years Up to 3 years Up to 3 years
Maintenance (calibration, sensor replacement) Annual system check Annual system check (Sensors should be replaced every 3 years or sooner depending on exposure to NH3 at calibration) Annual system check (Sensors should be replaced every 3 years or sooner depending on exposure to NH3 at calibration
Sensor Hot Swap N/A Plug and play pre-calibrated sensor modules for quick, simple sensor replacement Replaceable Sensor Heads
Sensor Range 25 - 10,000 ppm on one sensor 0-100 PPM
0-300 PPM
0-1,000 PPM
0-10,000 PPM
0-100% LEL
0-100 PPM
0-500 PPM
0-1000 PPM
0-10,000 PPM
0-100% LEL
User Interface Large graphic LCD display and on-board controls Mobile app interface with Bluetooth connectivity On board controls and LCD screen
Find out more Find out more Find out more

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