Lesson 4 - Health and Safety

There are two gases of particular interest to our learning objectives – ammonia and carbon dioxide. We will focus first on ammonia.

Ammonia

Anhydrous ammonia used in mechanical refrigerating systems is a flammable and toxic gas under ambient conditions, which is lighter than air. Under a pressure of approximately 10 bar at ambient temperature, it becomes liquid.

Ammonia is a toxic gas. It has a distinctive pungent odour and can normally be detected by smell at concentrations as low as 5 mg/L. This means that people, due to the smell, are unlikely to remain where concentrations are hazardous to health.

The generally recommended exposure limit for ammonia in the is 25 mg/L (8-hour TWA), and the short term exposure limit is 35 mg/L (10-minute TWA). Concentrations above 100 mg/L cause discomfort to most people and the U.S. Department of Health specifies that a concentration of 500 mg/L is immediately dangerous to life or health. Most people experience immediate eye and throat irritation between 400 to 700 mg/L. A level of 2,000 mg/L can be fatal after about 30 minutes exposure, and exposures to concentrations exceeding 5,000 mg/L (0.5%) are rapidly fatal. There have been a number of fatalities in the brewing industry from ammonia.

Skin contact with liquid ammonia or non-insulated pipework will result in burns. Eye contact with liquid ammonia will result in permanent damage if the eye is not properly flushed with water within 20 seconds of the exposure.

Ammonia leaks can also give rise to explosions. The flammable range of ammonia, in comparison to many other hydrocarbons, is high and narrow with a Lower Explosive Limit (LEL) of 15% and Upper Explosive Limit (UEL) of 28%. It is also slightly more difficult to ignite, and the rate of pressure rise and maximum explosion pressures of ammonia are lower than other typical hydrocarbons. Despite this, there have been a number of brewery fires and explosions involving ammonia.

In refrigeration systems, ammonia is liquefied under pressure. When liquid ammonia is released to the air, it will evaporate, and part of it will rise and disperse as a gas because it is lighter than air. The other part will absorb moisture from the air and form ammonium hydroxide. This dense white cloud will travel along the ground as an aerosol. If a sizeable release of liquid ammonia occurs, it can also form a spreading pool of liquid ammonia.

If a brewery has ammonia on-site, a full HAZOP of the entire ammonia system should be done and periodically reviewed.

Carbon dioxide (CO₂)

Large amounts of carbon dioxide are formed during germination and fermentation. However, many people do not realise the health and safety risk posed by CO₂: we breathe it in and out all the time. Outdoor air typically contains about 350 mg/L, which is not harmful to health.

At room temperature, carbon dioxide is a colourless, odourless, faintly acidic-tasting, non-flammable gas. However, CO₂ is heavier than air and can accumulate in trenches, sumps and basements, particularly below enclosed fermentation cellars. Not only will this displace the level of oxygen in the air, but CO₂ is toxic at higher concentrations.

Exposure to carbon dioxide can produce a variety of health effects. These may include headaches, dizziness, restlessness, a tingling feeling, difficulty breathing, sweating, tiredness, and increased heart rate. Fatalities from asphyxiation have occurred in the brewing industry when operators have been exposed to high concentrations in tanks and other confined spaces.

In many countries, CO₂ is classed as a substance hazardous to health, and the following workplace exposure Limits (WEL) are stipulated:

• Long term exposure limit (8-hour reference period) of 5000 mg/L

• Short term exposure limit (15-minute reference period) of 15000 mg/L