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Risk & Hazard Assessments

"Module 1"

Please note this article was first published in 2002, circumstances and events may have changed opinions. Jeff Charlton

Recovery from a Terrorist CBR Attack London Underground


This assessment looks at the various component risk and hazard regarding possible contamination and clearance solutions coupled to the acceptable clearance risk of public safety.

From the initial incident a clear hypothesis of acceptable clearance must be established. From the scale of potential contamination and possible ongoing risk, total 100% clearance may not be possible, therefore due to the necessity of the network facilities being required a lesser acceptability may be required.

The following assessments considers the exposure to hazard and risk in various format.

1.00 Human risk

  • LU employees
  • Passengers
  • Decontamination team
The need for LU employees to be onsite during both evacuation and decontamination is essential. This is due to their ability to manage the evacuation and provide specific knowledge regarding the facility. In my opinion they are unlikely to be available, due to low calibre untrained or ill equipped confidence.
Passengers are likely to leave the scene whether affected or not, creating the potential; for secondary effects of cross contamination.

In any event the passenger exposure to contamination of the various potential weapons will result in casualties and in some events the prognosis for recovery is low. It is therefore essential to consider secondary exposure and subsequent health risks which would revolve around containment and decontamination.

Decontamination teams need to be fully equipped and on site quickly to prevent or control the potential for spread. The availability of even minor ppe, such as filter masks and disposable paper suits to don in the event of contaminated clothing being removed may be essential for post incident confidence of returning passengers.

1.01 Environmental risk

  • Apparent or visible risk
  • Void or hidden
  • Potential future risk
Contamination may be in any form and may take days or weeks for effects to materialise. Clearly without an obvious incident there is possibility of attack being unknown to authorities, until symptoms develop. The requirement for total decontamination to allow stations or indeed the network to reopen may be impossible within acceptable time frames coupled to acceptable risk levels. Clearly a level of clearance may be required and this may be supported by the use of ppe by passengers following the re-opening of service. This need may be reduced due to continuing decontamination procedures out of hours during station closure or by the isolation or containment of possible contamination. There may be a potential for additional risk from transportable particulate becoming free and airborne at a later date. Therefore future controls, monitoring and passenger protective devices should be considered. This may take the form of ppe or permanently installed Heppa air scrubbing equipment which should be passenger visible.

1.03 Contamination

  • Chemical
  • Biological
  • Radiological

Chemical attack may not be an issue for control or limitation due to it’s effects which may be spontaneous or delayed. The various routes of body ingress, skin or inhalation make it’s effects almost uncontrollable. Following an attack cleaning and decontamination should follow planned procedures and dispersal , dilution may reduce secondary effects although the primary or initial effects may be catastrophic. The quantity of agent coupled to access may be a limiting factor.


The type of agent may be critical in decontamination protocol. Two types e considered, transmittable or contagious or static such as spores. The former may be readily reduced by the evacuation of the premises although secondary infection is the major concern. This could result in epidemic and therefore control and containment followed by prophylactic care is essential. The means and mechanism of government measures are unknown to the author. The second risk is from dormant agents which may become active following ingestion or inhalation. Typically anthrax is considered.

Two risks are assumed, the primary affects of direct infection and the secondary risk from contaminated clothing and the possibility of affecting those not involved with the primary event.

Risk reduction procedures such as personal decontamination and prophylactic care are considered.


While inhalation of irradiated particulate matter is the main concern the identification and subsequent decontamination is the easiest of all decontamination procedures. Affected persons will be confirmed by hospitals and again secondary irradiation by transportable particulates is a major concern. Removal of contaminated clothing at the scene is required and temporary lock down of contamination is required to prevent spread.

1.04 Clearance criteria

  • Current
  • Future
Passenger confidence in the safety of the network may be substantially reduced following an incident. Clearly there will be a priority requirement to prove safety in the network use. This may be initiated from the observed response to any incident but subsequently from scientific independent evaluation of decontamination. The initial acceptable clearance may be issued however due to the potential for reservoirs hidden in ventilation systems, tunnels, cavities etc, the potential for re-contamination must be considered.

While ongoing works or indeed closure may be considered there will I believe be a requirement to re-open the network at the earliest possible, safe, opportunity. This may be dictated by government requirements but subsequent press or independent assessments may require ongoing monitoring to substantiate any safety statements.


The potential hazard is high although the risk of attack may initially be assumed to be low. However in the event of any level of attack all assessments rise to the highest level. It is assumed that due to the potential of attack in any form or indeed at any location that government or local authority resources are low due to dilution from dispersal.. This may mean that due to delay, all risks become unmanageable and escalate. There is a clear need for contingency planning which should include the benefits of commercially available resources.
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