• The LPG supplier has changed its policy on the inspection of underground pipe work since the incident and has reviewed their underground pipe work inspection procedure. This is to include decommissioning of a line to allow a pressure test. • Manual recording is not sufficiently accurate to reliably identify stock losses from leaks and consequently the petrol company involved are trialing a new electronic monitoring sheet which would identify leaks on a daily basis. If the trial is successful, the sheet will be rolled out to all sites on the network.
Discussion
ARTICLES
The causes of accidents/dangerous occurrences can be classified into immediate, underlying and root causes. By considering these collectively a picture of why the accident occurred can be built up.
Immediate Cause This is the most obvious reason why an adverse event happens. The immediate cause of the incident was an ongoing leak of LPG gas from a damaged supply pipe which found its way into the base of the electric meter cupboard, forming an explosive mixture which appears to have been ignited by an electrical spark.
Underlying Causes These are the less obvious system or organisational reasons for an adverse event. In this case the underlying causes are: 1. damage occurring to the underground pipe and this damage going undetected. This initial damage, at least in part, may be due to the pipe not being installed in accordance with the manufacturer’s instructions. 2. the failure to properly identify the cause of the gas smells at the premises during July and August 2008. 50
3. The ability of the leaked LPG to migrate through ducting and into an area where it could form an explosive mixture and be exposed to a source of ignition.
3. Wet stock monitoring systems at the time of the incident were not designed to identify leaks of LPG and ways of improving the sensitivity identifying
Root Causes The Root cause is the initiating events or failings which led to all other causes. These are generally management, planning or organisational failings.
of
this
means
leaks
should
of be
progressed. 4. At the time of the incident, systems for the inspection and maintenance
of
the
LPG
installation at the premises were 1. Failure during construction to properly manage the installation of the underground pipe and possibly any work subsequent to this installation.
apparently in line with similar regimes
across
although
the
there
industry
was
no
satisfactory system to identify the condition and integrity of the underground LPG pipe work.
2. There was no system to leak test underground pipe work following repeated reports of LPG smells.
Failure rates on underground pipes are currently reported to be low, but in the event of such a failure occurring, the potential
3. Failure during construction and subsequent site checks to ensure ducting leading from the man hole chamber into the building was adequately sealed.
for high risk situations developing is high. As underground pipe work
older,
the
higher due to the effects of
Conclusions and Recommendations
corrosion, particularly on defects which
1. The explosion resulted from a damaged and leaking underground pipe which allowed gas to migrate through an unsealed electrical duct into the electrical meter cupboard where it was ignited. Operators and regulators therefore need to ensure that pipework is properly installed and that all ducts and similar pathways are sealed to prevent flammable vapours from migrating into areas where they could cause hazards.
occurred
installation
or
during following
subsequent damage. Where there is any uncertainty surrounding
emergency
response for reported LPG smells it is recommended that the presumed action should lean towards
testing
underground
pipe lines. Routine testing of lines should also be considered as part of a routine maintenance system
2. It is likely that the damage to the pipe occurred around the time of the construction of the site and that subsequent corrosion allowed gas to leak, probably becoming significant at some point during the first half of 2008. Consequently, monitoring of the installation and any subsequent ground work or vehicle movements near this type of pipework needs to be carefully managed.
becomes
potential for failures becomes
for
the
overall
LPG
installation.
Note This report is partly based on the internal
investigation
provided
by
following
the
the
oil
incident
report company as
the
Petroleum Licensing Authority did not investigate until some time after the incident by which time the physical evidence on site was no longer available.
APEA tel/fax 0845 603 5507 www.apea.org.uk
