Leaks and Response in Ammonia Refrigeration Systems

Why is ammonia both an efficient and a risky refrigerant?

Ammonia is a refrigerant widely used in food facilities that need large refrigeration capacity, such as cold stores, dairy and meat processing plants, and ice cream and frozen food production. Its refrigeration efficiency is high; but an ammonia leak is one of the most serious scenarios in a workplace's emergency plan.

The properties of ammonia that need to be known from a workplace safety point of view are:

It is corrosive and irritant. It can cause severe damage to the eyes, skin and respiratory tract. Contact with liquid ammonia also causes cold burns.
Its sharp smell gives early warning, but it is not a reliable measure. It is noticeable even at low concentrations; however, the sense of smell soon becomes accustomed to it, and smell is no use for estimating concentration.
As a gas it is lighter than air, so in enclosed spaces it tends to collect towards the ceiling. When it leaks as a liquid, however, it can form a cold, dense cloud that spreads close to the ground.
It is flammable at high concentrations. The choice of electrical equipment in the plant room is therefore important.
It dissolves very readily in water. This property is used in response, but spraying water directly onto a pool of liquid ammonia can increase evaporation.

Annex 1 of the Regulation on Health and Safety Measures for Work with Chemical Substances gives the 8-hour occupational exposure limit value for anhydrous ammonia as 20 ppm (14 mg/m³) and the 15-minute short-term limit value as 50 ppm (36 mg/m³). These values apply to normal work; during a leak, the concentration in the area can rise far above them.

Where do ammonia leaks occur? From the plant room to the evaporator

Leaks usually start at connection and intervention points:

Valve packings, flanges and unions
Compressor shaft seals
Safety valves lifting
Draining from oil collection pots during oil removal
Evaporator coils and pipework in cold rooms
Pipes damaged by forklift or load impacts
Opening the line for maintenance

Two lines on this list are routine jobs: oil removal and maintenance. These jobs require written instructions, working in pairs and a work permit; see the permit-to-work system. Protecting pipes in cold rooms against forklift impacts is also part of warehouse traffic management. For other risks of working in cold stores, see our article on working in cold stores.

Ammonia detectors and staged alarms

Because smell is not a reliable warning, the foundation of ammonia refrigeration safety is fixed detectors. The detector plan should answer these questions:

Where? Near likely leak points, in the upper part of the plant room and in cold rooms containing evaporators.
How many stages? At a low level, a warning and ventilation coming on; at a high level, an alarm, evacuation and the system moving to a safe state as designed. Alarm levels are set by the system designer in accordance with the relevant standards.
Where is the alarm heard? Not only in the plant room, but also at the gatehouse, where the shift supervisor is and in areas left unoccupied at night.
How is it tested? Detector calibration and function testing are carried out according to the manufacturer's instructions and recorded.

Plant room ventilation and emergency stop

The plant room is where a leak is most likely and most concentrated. The following points are checked in design and daily operation:

Emergency ventilation: A fan that runs automatically with the detector and can be started manually from outside. The fan and motor must suit the explosive atmosphere assessment; this assessment is part of the explosion protection document.
Stopping from outside: Buttons that stop the compressors and cut the necessary electrical sections must be outside the plant room door, labelled and easy to reach. Nobody should go inside to press this button during a leak.
Discharge point: Air discharged by the emergency ventilation must not be directed at areas where people gather or at ventilation intakes.
Doors and layout: The escape route from the plant room is kept clear; the room is not used as a store or workshop.

Under Annex III of the Work Equipment Regulation, ventilation installations are subject to periodic inspection at least once a year. Set the inspection scope and interval for pressure vessels in the refrigeration system according to the tables in the same annex.

Emergency equipment: what should be where?

Equipment being left inside during a leak is the most common planning mistake. The basic rule is: response equipment is kept outside the plant room, close to the entrance.

Equipment	Where should it be?	Note
Self-contained breathing apparatus with compressed air cylinders	Outside the plant room, close to the entrance	For the team entering the leak area; users trained
Full-face mask with a filter suitable for ammonia (type K)	Outside, easy to reach	For escape and low concentrations; not sufficient at high concentrations or in oxygen-deficient atmospheres
Chemical protective suit, gloves and boots	In the cabinet outside	Against splashes of liquid ammonia
Eyewash and emergency shower	Close to the plant room exit	Protected against freezing and tested regularly
Wind direction indicator	On the roof or in the yard, visible from the assembly point	For choosing the direction of evacuation
Emergency stop and isolation buttons	Outside the plant room door	Labelled
System diagram and valve list	At the entrance and in the emergency file	Which valve isolates which section
Detector alarm panel	Where it is always visible	Alarm log kept

Evacuation and response sequence in a leak

The Regulation on Emergencies in Workplaces requires response and evacuation methods, responsible persons and shut-off points to be included in the emergency plan. For an ammonia leak, the plan should follow this sequence:

Move away and raise the alarm. The person who smells the gas or hears the alarm moves away from the area towards the direction the wind is coming from and raises the alarm.
Stop from outside. Without entering the plant room, the person responsible stops the compressors with the buttons outside and checks that the emergency ventilation is running.
Evacuate and count. The department or building is evacuated. The assembly point is chosen according to the wind direction; the plan should therefore have at least two assembly points. A roll call is taken.
Call for outside help. 112 is called; the location of the leak, its estimated size, the wind direction and whether anyone is still inside are reported.
Only a trained team responds. At least two people enter the leak area with self-contained breathing apparatus; a back-up team with the same equipment waits outside. The leak is isolated with valves according to the system diagram.
Use water correctly. A water curtain can be used to knock down vapour; water is not sprayed directly onto a pool of liquid ammonia. Ammonia-contaminated waste water is prevented from entering the sewer.
Do not return without measuring. Return to the area takes place only after measurements show that the atmosphere is safe. The incident is investigated and the risk assessment reviewed.

Whether the plan works can only be seen in a drill. A drill is held at least once a year; be sure to include the ammonia leak scenario in one of these drills. For preparation, see our article on emergency drills.

Ammonia poisoning: the first minutes of first aid

In ammonia poisoning, the aim of first aid is to end exposure immediately and limit the damage until help from 112 arrives:

The person is moved to fresh air once the rescuer has ensured their own safety.
The eyes are rinsed with plenty of water for a long time, keeping the eyelids open; contact lenses are removed if present.
Contaminated clothing is removed and the skin washed with plenty of water.
Areas frozen by liquid ammonia are not rubbed.
Because symptoms can worsen later, a person who feels well is also assessed at a healthcare facility.

For general response principles in chemical spills, see our article on chemical spill response.

In its emergency plan and risk assessment work for food facilities in Bursa and the surrounding provinces, Bursa Sistemer treats the ammonia leak scenario as a separate heading. Other risks in the sector are on our food page; you can track drill and periodic inspection dates with the OHS calendar tool.

Frequently Asked Questions

Which mask is used in an ammonia leak?

The team entering the leak area uses self-contained breathing apparatus with compressed air cylinders. A full-face mask with a filter suitable for ammonia is for escape and low concentrations; it is not sufficient at high concentrations or in oxygen-deficient atmospheres.

Where is an ammonia detector installed?

Near likely leak points, in the upper part of the plant room and in cold rooms containing evaporators. Placement and alarm levels are set according to the system design and the relevant standards.

How is the assembly point chosen in an ammonia leak?

According to the wind direction. The plan should therefore have at least two assembly points in different directions and a visible wind direction indicator.

If we cannot smell anything, is the area safe?

No. The smell of ammonia is noticeable at low concentrations, but the sense of smell soon becomes accustomed to it. The safety of the area is confirmed by detectors or measurement.