Ammonia detection by laser, the next generation of ammonia detection

Ammonia was amongst the world’s first chemical refrigerants.
Due to it’s low cost, efficient cooling qualities and environmentally friendly credentials it remains one of the most popular, particularly for industrial and heavy commercial applications including cold stores, commercial fishing boats and meat processing plants. Ammonia, however is also harmful, even at low levels of exposure. According to the UK’s Health Protection Agency’s (HPA) Compendium of Chemical Hazards (PDF, 260 Kb) “Minor exposures may result in a burning sensation of the eyes and throat and more substantial exposure may cause coughing or breathing difficulties.” Very high exposure can be fatal and long term injuries to a high number of exposed personnel are not uncommon. NIOSH “Pocket Guide to Chemical Hazards.” lists the following exposure limits.

  • TWA (Time Weighted Average): 25ppm
  • STEL (Short Term Exposure Limit): 35ppm
  • IDLH (Immediate Danger to Life & Health): 300 ppm
  • LEL (Lower Explosive Limit): 15%

A review of media reported incidents by the European Fluorocarbon Technical Committee (EFCTC) showed that ammonia leaks cause 140 injuries and 14 deaths a year. Due to the large volumes stored on premises and its vaporous nature, ammonia leaks are also frequently in the headlines often causing evacuation of the local area. These attention grabbing events adversely impact a company’s reputation and its standing in the community. In response to these health and safety risks, regulators are tightening compliance regimes. In addition to rigorous health and safety laws making company directors more accountable for the safety of their staff, standards are being introduced in many geographies specifically for the management of ammonia. This means that company leadership needs to be forward thinking to prevent exposure to litigation.


Current ammonia detection methods fall into 3 broad categories.


Chemical gas detectors work by allowing gases to diffuse through a porous membrane to an electrode where it is either chemically oxidized or reduced. The amount of current produced is determined by how much of the gas is oxidized at the electrode, indicating the concentration of the gas. It’s primary advantage is its low upfront cost of between $1,000 and $3,000 per sensor. It’s also easy to install.

However, there are several challenges posed by this detection method, which include:

1. Frequent false alarms

Cross reactivity to other gases of similar chemical structure makes chemical sensors prone to false alarms. A false alarm can lead to loss in production time (at least 60-80 mins while site evacuation occurs, the alarm is investigated and the all clear is given) which can lead to financial losses (e.g. a typical meat processor produces around 200 kgs/minute) plus overtime payment to cover the targeted deadline.

2. Requirement for regular maintenance

Plant rooms usually contain a low level of background ammonia at sub alarm thresholds. This background exposure is continually reacting with chemical sensors, depleting the sensor itself. This results in recalibration on a regular basis. It’s not unusual for sensor maintenance to be required quarterly or in less demanding environments bi-annually. This maintenance does however result in an ongoing cost which can be as high as $1,000 per sensor per year. It can also be a logistical burden to the operation. The calibration process sometimes requires the sensors to be taken to an off-site facility which renders the site vulnerable to volatile gas leaks.

3. Dead sensors

Most operators switch off their ammonia sensors during periodic high concentrations of ammonia e.g. oil flush in an engine room (which can cause concentrations up to ~200 ppm). Whilst switching the alarm off prevents a false alarm it doesn’t protect the sensor from degrading in the presence of the high levels of ammonia. If a sensor is exposed to enough ammonia, or similar volatile gas, the sensor will be rendered dead. Replacing sensors is costly and will eat into capital expenditure.

Chemical sensors behave like a battery. They have a definitive usage limit measured in ppm/hours. For example, if an ammonia cell is rated for 10,000 ppm/hours that means it can be exposed to 5,000 hours of 2ppm ammonia or 1000 hours of 10ppm. Exposure to a significant amount of ammonia can render all the devices on the site ‘dead’ requiring capital expenditure to replace.


Solid state, or catalytic gas detectors are typically constructed from a treated wire filament which becomes oxidised upon exposure to a volatile gas. A reference cell is used to indicate the change in resistance generated by the heat which is proportional to the concentration of combustible gas. The advantage that solid state detectors offer are low price with easy installation. They also however share similar challenges to the electrochemical sensors i.e. frequent false alarms, maintenance costs, regular calibration, sensor replacement, lag in response times etc.


Because ammonia has a recognisable odour it has, in the past, been easy for plant operators to lean on their staff to detect the smell of ammonia. The advantage this offers is it’s up front cost efficiency, zero dollars. There are however several distinct problems with this option.

1. Olfactory Variety

Most agree that ammonia has a powerful scent, but not everyone agrees on how much ammonia is present by the time we can smell it. The Odour Threshold for ammonia has been documented in different studies as low as 0.04 ppm and as high as 57 ppm. For example: The US Coast Guard Manual says the Odour Threshold for ammonia is 46.8 ppm The American Association of Railroads says most people can smell ammonia between 0.04 to 20 ppm.

2. Olfactory Fatigue

Olfactory fatigue is a common occurrence with many volatile chemicals including ammonia if workers are constantly exposed to low ambient levels of ammonia their ability to detect a larger more significant quantity may be compromised.



Photonic Innovations Ltd (PIL) laser sensors are programmed to lock onto a unique absorption feature of the target gas, in this case ammonia. This renders an extremely high detection fidelity. This technology allows it to avoid the false alarms common in chemical sensors that occur due to cross gas reactivity and sensor depletion.

PIL’s laser sensors are not depleted upon exposure to ammonia and other toxic gases. This means that frequent maintenance/calibration is no longer a requirement.


PIL’s laser sensors are not depleted upon exposure to ammonia and other toxic gases. This means that frequent maintenance/calibration is no longer a requirement. With no filaments or chemical components, you only require functional testing which should be carried out by an accredited person.


Market leaderPIL’s laser sensors monitor ammonia concentration in the engine rooms at all times without degrading due to prior exposure. This means response time is consistently high. When tested against a market leading ammonia detector (fixed module) as seen in figure 1 below, PIL’s FLD 4000 (blue curve) responded an order of magnitude faster than the market leading ammonia detector (green curve); an important aspect when a massive gas leak or an explosion could be seconds away. PIL correlated the FLD 4000’s ammonia detection capability against a hand held ammonia detector at one of their client’s sites (see figure 2 below). Every engine room periodically flushes its pipes and valves with ammonia which results in an artificial ammonia leak (mostly >100 ppm). Old engine rooms often have a constant background of ammonia as a process byproduct (< 10 ppm). Both of these ammonia concentrations can result in gradual death of the electrochemical sensors. The graph shows PIL FLD 4000’s ability to register every rise and fall in ammonia concentration. The hand held detector’s old sensor recorded the peaks in ammonia but failed to register every background event.

PIL laser based detector offer a significantly faster response time and a greater sensitivity to the volume of the targeted gas.

Photonic Innovations Ltd (PIL) laser sensors are programmed to lock onto a unique absorption feature of the target gas, in this case ammonia. This renders an extremely high detection fidelity.


OPLD 4000 records a routine background concentration of ~5-10 ppm at a client’s siteThe current crop of ammonia detectors offer a low up front investment and a significantly less compromised mechanism for gas detection than the human nose. Compared to laser based gas detection, they bear a high maintenance burden and, due to their depletive qualities, demonstrate slower response time and a degree of unreliability between calibration cycles. The result of this can be false alarms which has a knock on effect on productivity. The slow response time may also compromise how effective avertive action may be in response to an emergency.

PIL’s laser based detector offers a significantly faster response time and a greater sensitivity to the volume of the targeted gas. Safety of workers is improved and the integrity of business is preserved.

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please contact:
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