Safety Alert
From:
Ref No
Date:
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.