Site Evacuation

Safety alert outlining reason for site evacuation after ammonia leak 


                                                       Safety Alert



Ref No 




Open System Leads To Site Evacuation



Distribution:       Work Place notice boards together with discussion at safety meeting



A large distribution centre was evacuated when the leak detection equipment alerted site security staff to a leak of ammonia in the plant room.


The leak was genuine, and had to be stemmed by the engineer accompanied by two Firemen wearing breathing apparatus.


The leak was from a broken ¾'' NPT nipple. The nipple had connected the dual port relief valve assembly to the oil separator and had split around the threads, leaving a portion of it stuck inside the connection on the separator. 


The leak occurred during the evening, three hours or so after engineers who had been working on repairing the nipple had left site for the day. The separator was left pumped down, valved off (one valve in each live connection) and the drive motor electrically isolated, but left open to atmosphere (as the nipple had not been repaired).


The leak occurred either due to one of the isolating valves passing or due to ammonia boiling out of the oil in the separator because the oil tank heaters were still operative.


On this occasion the leak was minor, the detection worked and no one was put at serious risk, but the potential existed for a major leak. Plant should only be left open to atmosphere in exceptional circumstances and only then after authorisation by a manager.


If plant has to be left open:


• All the openings must be fitted with blanks or

• Must be isolated with two shut valves in every line.


If the above is not possible, special arrangements are to be made by the manager or supervisor.


Carry out a Risk Assessment and produce a method statement to include, but not limited to, the following controls:

 Ensure leak detector and alarm system monitoring are working.
 Put ventilation systems on manual full vent for the unattended period.
 Arrange with site for periodic checks through the unattended period. 

Last modified: Thursday, 4 July 2013, 9:48 AM