Safety Incident Topic: Lost Of Containment from Hose
Location Of Incident: Hull, UK
Date Of Incident: 30 April, 2005
Brief Account Of Incident
After the 7-day campaign of the S522 evaporator was complete, an attempt was made, as per procedure, to blow the contents to a storage tank using nitrogen pressure, but solids in the outlet line prevented this. Operators tried several methods to unblock the pipe without success, and eventually connected a steam hose to the pipe to try to clear the blockage. This method had been used successfully in the past. Over the next 4 hours the hose was checked frequently, and there were no leaks, but then the steam hose coupling parted. Approximately 2.5 tes of flammable liquid (50% butyl acetate/50% acetic acid) were released from about 8 metres above ground. The liquid flowed down over pumps and equipment below for about 15 minutes, but did not ignite.
The hose connection was a BOSS type. The female part of the coupling was seized. When operating correctly, the coupling can be tightened without moving the hose. Because the female part was seized, it is believed that the action of uncoiling the hose, and other movement when condensate was drained, had gradually unscrewed the coupling.
This connection should rotate freely to allow assembly but it was found to be seized onto the female side of the coupling
What Went Wrong (Critical Factors)
· Defective Equipment: The hose coupling parted, due to inadequate design and/or maintenance.Inadequate Identification of Safe Behaviour/Poor Judgment: Use of steam to clear blockages on acid plants is a relatively routine activity. The operators did not appreciate the hazards of this task, and there was no written procedure or risk assessment.
· Site rules require that if a hose is to be used in a ‘closed circuit’ then the Group Engineer should be asked whether Management of Change review is required. This was not done.
· Following Procedures: The use of hoses did not comply with site procedures.
· Inadequate Implementation of Policies, Standards and Procedures: Site rules on the use of hoses had been significantly changed in 2003. The changes were communicated, but this appears to have been ineffective, since knowledge of the new rules is inadequate, and some of the necessary modifications to equipment have still to be implemented.
What Went Well
.Response to the incident by operators and the site emergency response team was excellent. .Foam was applied, and the liquid was contained within the plant and recovered.
· The design and maintenance of the hose couplings will be reviewed.
· The requirement for risk assessment of potentially hazardous tasks requires re-emphasising, especially for tasks that are not covered by operating procedures and are infrequent or non-routine.
· The method of communicating changes to site rules requires improvement.
· Management audit systems need to include audits of compliance with site rules.
The operators were working very hard to find a way of unblocking the line. However the risks of this relatively routine activity were not adequately identified – there was no operating procedure, and no risk assessment was carried out.