Poor rating for 2013 is due to a site wide power cut on 30
October, which led to the opening of the bypass (so that the hot
gases are diverted away from the abatement plant to prevent a
fire). Some of the hot gases will still exit via the normal stack
and therefore register on the monitoring equipment. A further
similar event occurred on 11 December.
This is a technical breach of the legislation, however, the
environmental impact was minimal each time. The opening of the
bypass is a safety requirement to prevent fires; However, under the
CAS scheme, more than 1 gross incident in a year, where the bypass
opens, and the emissions register above the ELV by more than 2 x
the limit, drops the Operator from being classed as 'Good' to being
classed as 'Poor' immediately.
Because the bypass valve is held closed only whilst electrical
power is available, it automatically opens as soon as the power
goes off, even if this is only for a fraction of a second, and the
whole system will take around 10 mins to reset. Further
investigative work into preventative options is required.