“Our sympathies go out to families affected by the recent tragic incident at Carlsberg brewery in Northampton. This focuses our minds on the dangers of Ammonia, both in gaseous (anhydrous) and liquid form (anhydrous or aqueous).
Although loss of containment of this highly toxic substance can quickly lead to burning sensations of the eyes, nose and throat, and more serious respiratory conditions, there are other characteristics that require consideration under DSEAR:
1) Corrosion:
Ammonia, especially in the presence of moisture, reacts with and corrodes copper, zinc, and many alloys. Only iron, steel, certain rubbers and plastics, and specific nonferrous alloys resistant to ammonia should be used for fabrications of anhydrous ammonia containers, fittings, and piping.
Potential Hazards: • Release of ammonia due to excess water within a system freezing, which causes broken pipes and equipment. • Ineffective refrigeration due to excess oil within a system, causing the system to work harder than necessary, thus stressing the system components. • Oxygen levels of more than a few ppm in liquid ammonia or a few thousand ppm in gaseous ammonia can promote stress corrosion cracking in steels. o This may result in a catastrophic failure of bulk storage vessels. o This may result in ammonia weeping from a crack within a system. o Stress corrosion cracking proceeds more rapidly at high temperatures.
2) Flammability:
Although classified as a Flammable gas, both the minimum ignition energy at 14mJ, and auto ignition temperature at 630°C are high, giving a Gas Group of IIA and Temperature Class of T1. Due to these high figures, it is more likely that explosive mixtures of vapour and air will be ignited by burning or welding operations on incompletely purged systems, or high energy (fault) electrical sparks in poorly ventilated plant rooms. Ammonia vapour exposable concentration range is approximately 15% to 33%, or 110 g/m3 to 240 g/m3in air, but bearing in mind the lethal concentration is around 1,700ppm, or 0.17%, it is non-occupied, confined spaces with poor ventilation that are prime areas for consideration. Increases in pressure or temperature expand the flammable range, while increases in water vapour concentration narrow it. In outdoor storage or during transport it is unlikely to achieve combustible concentrations from aqueous solution.
When classification of equipment is being considered, account must be taken of the maximum possible spill and of the existing ventilation. The question of toxicity must rule out any work space being considered as Zone 0 or Zone 1, but the possibility of an accidental spill may result in a Zone 2 classification. Lack of ventilation in a non-working area may result in a Zone 1 classification, but it is strongly recommended that all spaces where Ammonia may be present are ventilated so that either a Zone 2 or Non-Hazardous classification may be given.
Mesh Safety’s DSEAR consultant team has in-depth knowledge and experience with Ammonia storage and use in processes, and appropriate controls and safeguards. Further reading can be seen in case studies for http://www.dsearriskassessments.co.uk/case-studies/bernard-matthews/ and http://www.dsearriskassessments.co.uk/case-studies/moy-park/.”
