Open System Leads to Site Evacuation

Open System Leads to Site Evacuation 

A large distribution centre was evacuated when the leak detection equipment alerted site security staff to a leak of ammonia in the plant room. This resulted in the local Fire Brigade attending site.  This document outlines good practise to minimise this risk. 

Author: Star Refrigeration

                                                                                                 

                                                                                                            Open System Leads to Site Evacuation

A large distribution centre was evacuated when the leak detection equipment alerted site security staff to a leak of ammonia in the plant room. This resulted in the local Fire Brigade attending site.

The leak was genuine, and was stemmed by the duty standby engineer accompanied by two Firemen – all 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, some time 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 had been electrically isolated. However, the system had been left open to atmosphere because the nipple had not been repaired. This is contrary to best practice - which requires two closed valves or blank flanges in each live connection.

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 leak detection system worked and no one was put at serious risk. However, the potential existed for a major leak.

Plant should only be left open to atmosphere in exceptional circumstances and only once a proper risk assessment has been prepared and authorised by an appropriate 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.

• 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 periodic checks through the unattended period.

Last modified: Tuesday, 27 November 2012, 8:43 AM