MEDWAY COUNCIL COMAH OFF-SITE EMERGENCY PLAN ...

ABRIDGED - Medway Council Off-site Emergency Plan – National Grid Grain LNG Ltd.
without serious injury’. Escape distance is specific to people, and so is not
considered any further with respect to effects on the environment. Secondary
fires distance is defined as ‘the distance at which secondary fires may be initiated
by piloted ignition in buildings made of combustible materials such as wood’. The
threshold level for piloted ignition of wood is 12 kW/m 2 . Above this secondary
fires will occur if the receiving material is irradiated for a sufficient length of time.
Spontaneous combustion of grasses occurs with thermal radiation levels of
approximately 15kW/m 2 for approximately 15 minutes. Therefore, some
vegetation within this hazard range could be expected to ignite.
15.5.1 A secondary fire could present a more significant effect on the vegetation present
on the Medway or Thames Marshes Ramsar, SPA and SSSI Sites. Marsh
communities are usually resistant to burning, except in periods of exceptional
drought, because they are so wet. However, if the fire was severe enough to
damage the marshland, there is a potential for natural succession to give rise to
the development of a slightly altered habitat. Following an incident an
investigation would be undertaken to assess whether a MATTE had occurred.
Grain Pit is beyond the secondary fires hazard range, and is therefore unlikely to
be harmed by thermal radiation from the terminal.
15.5.2 The effects of fire on grassland and agricultural land, and the definition of a
MATTE have been discussed in previous paragraphs in 12.4.1, and the same
conclusions apply, although a considerable area may be affected, rapid post-fire
regeneration is expected.
15.5.3 It is not considered possible that a secondary fire would cause the soil off-site to
be heated to such a high temperature to cause sufficient damage to constitute a
MATTE. Similarly, the SAMs and Grade One listed buildings are beyond the
secondary fires hazard range from the terminal and are unlikely to be damaged.
15.5.4 The potential effects of fire on species have already been discussed in the
section on flammable gas clouds, and it is considered that the same conditions
would apply to a secondary fire. A post-incident investigation involving
consultation with the appropriate statutory conservation organisation would be
carried out to ascertain whether a MATTE had occurred.
16 Other Environmental Consequences of a Major Accident (extract from
National Grid Grain LNG’s COMAH Safety Report)
16.1 Gas Release - The release of gases produced by combustion of natural gas
(carbon dioxide, carbon monoxide, nitrogen oxides, and hydrocarbons) to the
atmosphere from an ignition scenario is not considered to be a significant
environmental effect, compared to the national releases of these gases.
16.1.1 Release of natural gas without subsequent ignition would result in the emission of
methane to the atmosphere. Methane is a significant greenhouse gas, with a
global warming potential 21 times greater than carbon dioxide. However, any
release of methane from the National Grid Grain LNG Storage site would not
contribute significantly to global warming. In terms of annual emissions of
methane from the UK, which are around 3,800,000 tonnes, release of the total
site inventory would be insignificant.
June 2011 Page 34 of 52