Using ammonia for refrigeration is effective, saves resources and is generally safe. However, because gas leaks cannot be completely prevented, ammonia monitoring is essential. An ammonia detection system reduces the risk of production downtime, protects employees, and can save seconds that make a difference in case of an alarm.

Ammonia Refrigeration:What should you keep in mind?

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A NATURAL REFRIGERANTAmmonia: Dairies, bottling plants, butcheries and produc-tion plants with a freezing tunnel cannot do without it. Low temperatures must be generated wherever food is produced or processed – during storage, for preservation, or for spe-cial technologies and processes.

Chemically known as NH₃, ammonia has been used for this purpose for over a hundred years—used for the first time by Carl von Linde in 1870 to refrigerate beer. Today, the alkaline compound of nitrogen and hydrogen dominates the refrigeration system market now more than ever. This is because the natural refrigerant has a number advantages. Ammonia has a good volumetric cooling capacity and is a very effective refrigerant due to a heat of vaporization of 1368 kJ/kg.

Only a small amount of ammonia needs to be moved in the system—approximately 13 to 15 percent compared to fluo-rocarbons—to generate a high refrigeration capacity. This makes NH₃ very economical. But not only is the installation of an ammonia-based refrigeration system about 10 to 20 percent cheaper than similar systems, operating costs are also significantly lower.

Another advantage is that ammonia is more environmentally friendly than liquid hydrocarbons: Its global warming poten-tial (GWP) and ozone depletion potential (ODP) equal zero.

AMMONIA IN REFRIGERATION SYSTEMSTHE MOST IMPORTANT FIGURES AT A GLANCE

Molecular Weight 17.03 kg/kmol

Boiling point -27.94 °F/ -33.3 °C

State of matter under normal conditions gas, liquefies under pressure

(8.6 bar at 20 °C)

Lower explosive limit* 15 vol. percent

Upper explosive limit* 28 vol. percent

*at 68 °F and 1013 mbar

Ignition temperature 650 °C

Odor Detection threshold 5 ppm to 50 PPM (OSHA)

Draeger XS Sensor threshold 3 PPM

Draeger XXS Sensor threshold 1 PPM

OSHA PEL 50 ppm TWA

ACGIH STEL 35 ppm

TLV 25 ppm

NIOSH REL 25 ppm TWA

ILDH 300 ppm

Deadly concentration 5,000 ppm

Source: OSHA; CDC; NIOSH; www.euroammon.com; www.vfdb.de

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Ammonia

Chemical formula: NH₃Appearance: Colorless gas

AMMONIA REFRIGERATION: WHAT SHOULD YOU KEEP IN MIND?2 |

RISKS INVOLVED WITH AMMONIA REFRIGERATIONWhile ammonia is one of the most widely produced chemicals—more

than 130 million tons are produced annually, and growing—the substance

poses significant hazards.

1. Risk of explosion and fireAmmonia is a flammable gas and can form flammable or potentially explo-

sive compounds in dry air when in a gaseous state. The concentration

threshold is between 15 and 28 vol. percent. However, the required igni-

tion temperature is rather high—at least 1202 °F/650 °C. (www.euram-

mon.com)

NH3 is generally lighter than air and reaches the atmosphere with a high

diffusion velocity. In confined spaces and containers, it can displace any

available oxygen. NH3 has a high affinity for moisture and quickly forms

compounds with the moisture in the atmosphere. If ammonia leakages

occur, water curtains are used to damp down vaporous ammonia. The

gas then sinks to the ground in the form of ammonia aerosol, which is

visible as a white mist.

Ammonia has a relatively low flammability and only burns continuously if

there is a flame. If the steam content in the air exceeds 11 vol. percent,

flammable and potentially explosive mixtures are no longer possible.

Despite the extensive use of ammonia around the world, explosions and

fires purely caused by NH3 are very rare. Any known incidents occurred

almost exclusively in closed rooms or containers. Thus, there is only a risk

of explosion if the concentration in unventilated rooms exceeds the explo-

sion limit (15 vol. percent) or if high-energy ignition sources are present.

Maintenance work at ammonia refrigeration systems requiring welding,

soldering or cutting must be performed with extreme caution: existing oil

mists can lower the explosion limit of NH3/air mixtures. NH3 systems

should therefore be purged with air or a non-flammable gas prior to start-

ing the welding work in order to remove residual ammonia.

Another safety concern is the corrosive effect of ammonia on iron, cop-

per, zinc, tin and their alloys. Leaks can damage parts of the refrigeration

system and cause uncontrollable gas leakages. Corrosion caused by

ammonia not only causes perforation in the form of holes, but also as cor-

rosive cracks. These cracks are often very subtle and difficult to detect.

2. Toxic dangers to humansAmmonia is a respiratory poison that has a strong irritating and corrosive

effect—mainly in the liquid state. The strongest reaction occurs with

moist body surfaces such as the mucous membranes and eyes, causing

painful chemical burns. Inhaling ammonia can damage the respiratory

tracts and lungs.

If liquid ammonia comes in contact with the cornea, it can cause blind-

ness. Because the temperature of liquid ammonia is below -27.4 °F / -33

°C, it causes severe frostbite if it comes into contact with the skin.

Symptoms of minor ammonia poisoning include a feeling of suffocation

and breathing difficulties, dizziness, a burning sensation in the throat,

increased salivation, stomach ache and vomiting. Extended exposure

to liquid ammonia damages the respiratory and digestive organs. In

some cases, serious symptoms may appear hours after inhalation.

Contaminations at a level above IDLH(300 PPM) or higher are life threat-

ening.

Nevertheless, fatal accidents involving ammonia are rare. Due to its

distinctive acrid smell, which can be noticed in very low concentrations

starting at 5 ppm, humans normally notice it well below the threshold of a

harmful concentration.

This has both advantages and disadvantages. Ammonia’s low odor thresh-

old can cause panic among the employees, even if the concentration is

not dangerous. This is also one reason why reliable and precise detection

is essential: it helps to prevent uninformed and impulsive reactions.

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AVOIDING ACCIDENTS THROUGH EARLY LEAKAGE DETECTIONEven if the ammonia refrigeration systems are professionally and properly

maintained, accidental ammonia leakage can occur for many reasons—

such as corrosion, leaking valves, operating errors. Cracks frequently

develop when liquid residual ammonia is locked in pumps or lines during

standstill, which warms up and expands as a consequence. Other critical

scenarios include filling, maintenance and cleaning.

In fact, experts estimate that leakage losses in complex industrial refrig-

eration systems amount to 2 to 17 percent every year, depending on the

age and condition of the system.**

It is crucial to detect leakages quickly. On one hand, any effort for

required refilling should be kept to a minimum to avoid damage to the

system and the products stored in refrigeration. On the other hand, any

interruption of production costs money—whether it’s a real alarm due to a

hazard or merely a false alarm. This is why ammonia leakages in particular

need to be detected with high precision.

AMMONIA LIMIT VALUES FOROCCUPATIONAL SAFETY AND PLANT SAFETY

WES (AUS & NZ) TWA 25 ppm 17 mg/m3

WES (AUS & NZ) STEL 35 ppm 24 mg/m3

OSHA PEL 50 ppm 35 mg/m3

ACGIH TLV 25 ppm 17 mg/m3

ACGIH STEL 35 ppm

TRGS900 MAK 50 ppm 35 mg/m3

DFG MAK 20 ppm 14 mg/m3

France VLE 50 ppm

GB LTEL 25 ppm

EU OEL-TWA 20 ppm

EU OEL-STEL 50 ppm

IDLH 500 ppm

Please visit www.draeger.com/voice for more information

** Refrigerant Loss, System Efficiency and Reliability – A Global PerspectiveST-

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PROPER INSTALLATION OF FIXED GAS MEASUREMENT EQUIPMENT

1. Position measurement points correctlyIn ammonia-based refrigeration systems, the transmitters of a gas mea-

surement system are normally installed in the compressor room and

near the valve stations to monitor the ends of pipes. The sensors in the

compressor room should generally be positioned at the ceiling, because

ammonia weighs about half as much as air and rises quickly after a leak-

age. Even if workers cannot smell ammonia in the lower section of the

room, the concentrations at the ceiling can be significantly higher. When

installing the transmitters, make sure that the sensors are not positioned

directly in the airflow to or from the evaporator.

2. Factor in potential disruptive factorsExtreme temperature fluctuations are prevalent in the compressor room.

Moisture can develop during air heating and cooling due to condensa-

tion, which can affect the performance of sensitive devices. Moisture

can also be generated during defrosting procedures at the evaporator. If

possible, sensors should be positioned in locations that provide the best

protection from these or other potential disruptive factors.

3. Keep sensor performance in mindBecause of freezing and fluctuating temperatures, moisture and corro-

sion, not every sensor is suitable for the challenging environment of a

refrigeration system. For a reliable measurement performance, it is critical

that the gas detectors are robust enough to withstand the wide range of

temperatures and other prevailing challenges. In addition, the sensors

must have a high level of precision in detecting ammonia.

4. Select correct alarm thresholdsA basic level with a low background concentration is often present in

ammonia refrigeration systems. In order to avoid frequent false alarms,

the defined alarm thresholds should be slightly above the Threshold Limit

Value (TLV) level. A high quality sensor will support reliable and precise

measurements and help minimize false alarms and production downtime.

5. Conduct regular maintenanceFor reliable and precise measurements, a gas detection system must be

calibrated regularly and receive proper maintenance at specific intervals.

This is even more important if the system operates under challenging

conditions, as it does with ammonia refrigeration. It pays off to invest in

higher quality service. Technicians with specialized expertise are faster at

noticing and fixing effects of aging and signs of wear. As a result, expe-

rienced technicians increase the reliability of ammonia detection devices

and extend their lifespan.

Ammonia system Gas + liquid

Compressors

Condensors

Ammonia tank (-8°C) NH

3

circulation pumps

Separator

Screw Piston

Liquid Evaporators

Cold storage rooms

A Typical Ammonia Refrigeration System

AMMONIA REFRIGERATION: WHAT SHOULD YOU KEEP IN MIND? | 5

TRUSTED SAFETY SOLUTIONS In the majority of ammonia accidents, the hazardous substance occurs in

gaseous form. If injured persons are in the contaminated area, their res-

cue is obviously the highest priority. Respiratory protection independent

of the ambient air is essential for firefighters and other emergency per-

sonnel. One important component is a head piece, which also protects

the eyes from contact with the contaminated atmosphere. In many cases,

gas-tight chemical protective suits are required in the hazardous area.

If liquid ammonia leaks from refrigeration systems, the situation becomes

more problematic. Upon contact with the skin, the temperature of the

liquid, which is -27.4 °F /-33 °C or lower, causes frostbite. The level of

severity depends on the contact surface and the amount of liquid. Basic

protective clothing cannot withstand the freezing cold liquid which cor-

rodes through the material. When starting the work, wearing a chemical

protective suit made of cold-resistant material is recommended. To pro-

tect the skin from frostbite, warming work clothes and woolen sock liners

and gloves should be worn under the suit.

Selecting the right filterEmergency personnel who work on a damaged system to detect leakages

should be provided with personal gas warning devices for safety reasons.

For work that involves the risk of leaking or rapidly escaping ammonia—

such as opening the refrigeration circulation system—personal protective

equipment should be used.

This includes:

– Full face mask with appropriate ammonia filter

(Identification color green) and integrated eye protector Link

– Protective gloves

– Rubber boots

– Protective goggles

In the case of an alarm, escape apparatus that are independent of the

ambient air support an organized evacuation of the plant. Filtering escape

devices that protect workers from toxic gases also help protect escaping

persons.

Special requirements need individual solutionsAmmonia-based refrigeration systems present a particular challenge for

safety management. Gas measurement equipment, personal protective

equipment, and escape equipment all require individual solutions that

consider all plant-specific factors.

Both new installations and the integration of new components into exist-

ing infrastructures require fundamental knowledge of basic chemical and

physical principles, technical parameters, and legal requirements—which

makes for a highly complex planning process. Expert advice will be worth

it every step of the way: during acquisition, installation, commissioning,

and maintenance.

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