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ENVIRONMENT REPORT
2015
page 48
The accidental chemical releases from 2010 to 2014 are also categorised by source and cause. Figures 33 and 34
opposite show annual variation in the same way as the oil releases, highlighting the anomalous, largest incidents
over the last five years and reflecting the unplanned nature of the releases. The unknown category encompasses
the accidental releases for which no source or cause information was given. Consequently, it is expected that
these figures may change in the future.
Between 2010 and 2014, production systems and related equipment contributed the majority (940 tonnes)
of all accidental chemical releases, with hydraulic systems and pipework infrastructure accounting for twelve
(190 tonnes) and 21 per cent (350 tonnes), respectively (as shown in Figure 33). The 2010 production systems and
related equipment proportion (73 per cent of the total 2010 mass) is notable as it is dominated by eight releases
of more than ten tonnes each. The largest of these is a release of 136 tonnes of a low hazard production control
fluid due to failure of a seal on a subsea template valve. This is the worst case release amount and contributes to
the relatively large (26 per cent) contribution of seal failure to the causes of incidents in 2010.
Accidental releases from hydraulic systems made up 14 per cent (90 tonnes) of the total in 2010, and the largest
release in this category was of a worst case estimate of almost 71 tonnes of low hazard production control fluid
due to an intermittent leak from a subsea hydraulic valve. In 2011, the majority of accidental releases were from
pipework infrastructure, dominated by one incident where an estimated worst case amount of 190 tonnes of
methanol were accidentally released due to the failure of a subsea pipeline during pressure testing. Methanol is
categorised as PLONOR. The 2012 production systems and related equipment bar is made up of 112 incidents,
21 of which were greater than one tonne and are all PLONOR, low or medium hazard chemicals. The largest was a
release of 139 tonnes of low hazard water-based drilling fluid from the wellbore.
2013 and 2014 data show similar trends in the breakdown of sources of accidental releases, and the largest in those
two years was the production systems and related equipment 38-tonne release of hydraulic fluid, as explained
on p46.
The most common cause (Figure 34) of accidental chemical releases between 2010 and 2014 was structural failure,
making up almost half (780 tonnes) of the mass released. Valve failure and seal failure make up 15 (250 tonnes)
and 10 per cent (170 tonnes), respectively. The dominance of structural failure is similar to that shown in the
accidental oil release trends and again includes those incidents for which limited information is provided.