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Safety operation of anhydrous ammonia equipment

Treating straw with anhydrous ammonia has many advantages, such as high efficiency, low cost, simplicity of operation and elimination of parasite eggs and weed seeds. However, anhydrous ammonia is toxic and explosive, so pressure containers are required for transport and storage. It is very important to follow relevant national regulations for safe operation. The basis of these regulations should be well understood. Explosions of ammonia containers happen occasionally and have resulted in persons injured or even killed. All persons working with ammonia must learn from these accidents.

Physical and chemical characteristics of ammonia, and safe operation

Ammonia is a colourless gas with suffocating and penetrating odour. Under pressure or at low temperature (-33 °C) it condenses to a clear liquid. The physical and chemical characteristics of ammonia are:

· Chemical formula


· Boiling point (at atmospheric pressure)


· Density of ammonia


· Density of anhydrous ammonia

0.617 (at 20°C)

· Solubility in water (at 15°C)

60 g/100 g H2O

· Vapour from 1 litre of anhydrous ammonia

1 000 litre

· Solubility of gas in 1 litre of water

700 litre (20°C)

· Explosion limits

15-28% (volume)

· Safe concentration

0.0001 mg/litre

· Toxic concentration

0.2 mg/litre

In the presence of water or steam, copper, zinc and aluminium, and alloys containing these metals, will be corroded by ammonia. These metals are therefore not to be used in ammonia equipment.

The pressure change in an ammonia container according to temperature is illustrated in Figure 6-33.

Figure 6-33. Ammonia pressure change with temperature

The chemical and physical characteristics of ammonia are the basis of the selection of ammoniation equipment and for safe operation:

Safety supervision of ammonia containers

In order to emphasize the management of pressure containers with explosion risk, Safety supervision regulations for gas bottles, Supervision regulations for pressure containers, and Management regulations for liquefied gas tank trucks have been promulgated by the National Council, the Ministry of Work and Personnel, and the Ministry of Chemical Industry. Clear regulations have been established for the design, manufacture, installation, usage and inspection or repair of pressure containers, as well as for reporting accidents.

Ammonia tank trucks and bottles are classed as medium-pressure container transport. As ammonia is very toxic, a container of more than 440 litre volume is a class II container, which can implies serious consequences in a explosion.

According to national regulations, the following points should be observed when using pressure containers:

Regulations for safety in straw ammoniation

Ammonia is toxic and may explode under certain conditions. The ammonia containers are classed as "pressure containers with risk of explosion." Treating straw with anhydrous ammonia can endanger life and health if not done correctly. It is therefore necessary to follow the precautions and regulations made by the Bureau of Animal Production and Health (MOA, 1990):

Safety operation requlations for straw ammoniation

· Operators must have the necessary training, pass the examination and obtain their qualification.

· Safety equipment available at the working site should include:

- an abundant supply of fresh water;

- filter masks with ammonia filters;

- gloves and boots made of rubber or another suitable material; and

- fire extinguishers.

· Each new ammonia container must have an accompanying quality certificate that is properly filed.

· Never overfill whenever adding ammonia to a container.

· In summer, do not put ammonia containers in the sun. In winter, if ammonia flow is low, move containers to a warm place. Never heat them with fire.

· During ammonia transport, storage and straw ammoniation, check containers and hoses for leakage or swollen parts. Stop operation to make appropriate repairs to damage if found.

· Ammonia bottles must be firmly secured to the vehicle during transport to prevent them from falling due to movement.

· Be sure not to hit or to roll ammonia bottles during loading and unloading, which should be done slowly.

· Screw and tighten valves during bottle transportation and storage.

· Transport of anhydrous ammonia and oxygen in same wagon and storage in the same shed is strictly prohibited to avoid danger of explosion.

· If there is still pressure in a container, do not repair or fasten any part under pressure.

· When ammoniating straw, first place the spear into straw, then open the valve.

· Open and close ammonia-injecting valves slowly. During ammonia injection the gas pressure must be below 0.8 Pa. Do not hit the ammonia bottle with any tool.

· Ammonia flow should stop when pressure drops to 0.05 Pa.

· The ammonia containers can not be used to store any other material without the written consent of the working department.

· Ammonia containers must be checked regularly.

· The operators must wear protective equipment, including rubber gloves and protective suit, and stand upwind from the ammonia source.

· If ammonia leaks to the air, people should lay down on the ground, cover their noses with a wet towel and move upwind.

· Fire is forbidden in the vicinity of the ammonia station and the site of straw ammoniation.

· If an accident occurs, it should be immediately reported to administration and labour departments.

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