Ammonia is one of the most highly produced inorganic chemicals and is used in a wide range of industries. 80% of the ammonia produced is used in agriculture as fertilizer, but it is also commonly used as a refrigerant as well as for the purification of water supplies and the manufacture of plastics, textiles, pesticides and dyes.
AMMONIA AS A REFRIGERANT:
For over 100 years Ammonia has been used as a refrigeration gas as it has no global warming potential or effect on the ozone level. The drawback of ammonia though is that it is extremely toxic, has a pungent odour and, in high concentrations, can be flammable. To avoid workplace injury and accident, a gas detection system is an essential risk-reduction measure.
A refrigeration plant room is always subject to small ammonia leaks with moving equipment, valves and joints, so a background of the gas can be expected. Gas detectors used in these areas should be capable of working in a constant background and the controller should potentially be capable of controlling the ventilation. Detectors used here will be capable of reading higher values than just the TWA (TLV), as high concentrations are a real possibility in this application.
Refrigeration plant rooms can vary from a small room requiring 1-4 detection points, to larger areas where multiple detection points would be required. As Ammonia is flammable, albeit difficult to set alight and only at high concentrations (15.4% v/v), it should still be monitored for explosion risk in any area where these levels could be possible. This risk should always be considered where large quantities of Ammonia are stored or compressed. The alarm point is generally set at 1% v/v at which point non-essential electrical systems can be automatically shut down by the gas detection system if required.
WHAT GAS DETECTION EQUIPMENT SHOULD BE USED?
In refrigeration plant rooms, either portable or fixed instruments, or a mixture of both, can be used depending on site conditions and alarms must be set at the Threshold Limit Value of the regional regulation. UK values as set out in the HSE’s EH40’s Exposure Limits documentation for Ammonia are TWA 25ppm and STEL 35ppm.
WHERE SHOULD GAS DETECTION EQUIPMENT BE POSITIONED?
When it comes to the positioning of gas detection equipment, it is important to remember that although Ammonia is lighter than air and should rise to the ceiling, this will only occur if the gas is at the same temperature as the surrounding atmosphere. With refrigeration gas this may not be true, so gas temperature at a leak point should also be considered.
Liquefied ammonia released during an incident presents other hazards. For example, liquefied ammonia has an expansion ratio of approximately 850 to 1, which means that on release to ambient air, a given volume of liquefied ammonia will expand 850 times and could potentially cover an extensive area. Such a release will also involve an aerosol phase, i.e. small liquid droplets, along with ammonia gas. When released, it will be very cold and consequently behave as a dense gas (even though it is normally lighter than air) until it is warmed. One of the main characteristics of this cold dense gas behaviour is that the vertical mixing is suppressed. This is due to a stable density layering effect, which generates a slowly diluting vapour cloud that hugs the ground. A release that travels along the ground rather than immediately rising into the air increases the risk of exposure to workers and others.
FLAMMABLE WITH A PUNGENT ODOUR
Released ammonia will rapidly absorb moisture from the air and will form a dense, visible white cloud at high concentrations. If there is no visible cloud, an ammonia release can be detected by its pungent odour at low concentrations. The odour threshold for ammonia is reported in the range 0.02- 50 parts per million (ppm). Ammonia may be a fire and explosion hazard at concentrations between 15 and 25% in air. If the airborne concentration of ammonia is within the flammable range (typically under confinement), it can be ignited by something as common as an electric spark from a switch.
WHAT ARE THE EFFECTS OF AMMONIA IN HUMANS?
Inhalation of low levels of ammonia will cause irritation to the nose, throat and respiratory tract leading to coughing, an increase in respiratory rate and respiratory distress may occur. Substantial exposures can cause burns of all depths in the oral cavity, nasopharynx, larynx and trachea, together with airway obstruction and bronchiolar and alveolar oedema. Exposure to a massive concentration of ammonia gas may be fatal within minutes. In November 2016, an engineer working at a Brewery site in Northampton was killed instantly when an ammonia pipe leaked in his face. A total of 22 people were hospitalised following the incident including 2 police officers and 9 firefighters who were involved in the rescue.
WHAT PRODUCTS DOES GFG HAVE FOR THE SAFE DETECTION OF AMMONIA?
Take a look here: https://gfggasdetection.co.uk/gas_type/nh3/
By GfG Gas Detection UK Ltd