Safe working and separation distances between active search operations, the task site contact point (CP) and the local population need to take into account the net explosive quantity of IEDs that are assessed as likely to be present. This separation provides mitigation in the event that an unplanned explosion occurs and is normally calculated with the use of IMAS Technical Note 10.20/01 Estimation of Explosion Danger areas.
In an urban area additional factors can increase or decrease the risk to personnel in the event of an unplanned explosion. These include:
Channelling of an explosive blast pressure wave between structures, walls and through windows and doors could focus its energy in specific directions. Secondary hazards such as fuel, gas, electricity supply and toxic chemicals that are abundant in an urban area may enhance the effects of an explosive blast, or affect the safety distance itself. Secondary fragmentation from buildings and structural failure. Channelling of an explosive blast pressure wave between structures, walls and through windows and doors could divert its energy. Safety distances of explosives have been assessed against the power of TNT. Home-made explosives (HME) may have a reduced relative effectiveness factor compared with most military and commercial grade explosives and this should be considered when assessing IED safety distances. Consideration should be given to the level of confidence related to the HME type that is present and the worst-case scenario. Walls and pre-existing structures (including specifically constructed blast mitigation protective works) occur regularly in urban environments and can significantly reduce the risk of high velocity primary fragmentation being projected from an explosive blast in the same way protective works do.
INCREASED RISK FACTORS
DECREASED RISK FACTORS
IMAS 09.13 Building Clearance provides the following guidance on how this risk to personnel can be mitigated:
The task must be planned and executed to reduce the potential number of casualties to a minimum should an unplanned explosion or structural failure occur. When conducting search within the confines of a building, the three-dimensional environment, along with the building’s construction type, should be considered. If there is a threat of victim operated IEDs (VOIEDs) there should never be more than one searcher per room, and it is further recommended that a separation of two interior walls / floors between searchers is maintained. This is detailed in IMAS 09.13 Building Clearance. There should never be a searcher in a room directly above or below another. At their basic level, safety distances are spherical. Current IMAS provide guidance that enables MA organisations to reduce working and separation distances based on mitigation. This could include both pre-existing structures and specifically constructed protective works. Consideration should be given to how the energy of a pressure wave will alter inside buildings and urban environments. Channelling between structures, walls and through windows and doors will mean it may be possible to reduce a safety distance in one direction but increase it in another direction where it is channelled. Expert advice should be obtained when secondary hazards are identified (fuel, gas, electrical supply and toxic chemicals) that may enhance the effects of an explosion. This may involve liaison with the NMAA, other implementing partners, as well as local services such as fire and emergency rescue.
MITIGATION
Introduction
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