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Last updated: 12 August 2009
3. Recovery principles and priorities
3.1. During the early response to the incident the local authority should establish a Remediation Working Group to prepare advice and recovery proposals for the local authority's management team to consider(18). The aim of the recovery strategy should normally be to return the environment to unrestricted use.
3.2. It is very difficult to make general statements about CBRN substances because of the wide range and variety of effects, toxicity and concentrations that could be deployed. However in general terms, the principal challenges of chemical, biological and radiological decontamination of the environment are that:
3.3. In practice local constraints, such as intervention actions already undertaken during the emergency phase, may strongly influence the practical choice of recovery techniques especially, where the permitted timescales for recovery are short because critical national infrastructure is affected. Also, when making decisions on recovery options there is a balance to be struck between maximising protection of people and protection of the environment, because these constraints may drive accepted levels of clean-up, and their associated environmental impacts, in opposing ways.
3.4. Factors influencing the recovery strategy
3.4.1 Detection and intervention timelines. Chemical, biological or radiological substances could be dispersed in a number of ways, not necessarily by the use of static containers or explosive devices. The immediate effects of a release, whatever its cause, of a chemical substance are likely to be noticeable more quickly than a biological or radiological substance. Biological substances may require an incubation period of several days before people become sick. The delayed onset of symptoms in a biological incident means that the area affected may be greater due to the migration of affected individuals. Exposure to radiological substances also may not produce any immediately noticeable health effects, resulting in contamination spread before it is detected by monitoring instruments.
3.4.2 Size of the affected area. The area of land that has been contaminated to a significant degree by a chemical substance will normally only stretch a few hundred metres from the original release point. However the hazard zone will be larger than the contamination area because of evaporation or resuspension into the air of the substance. This is especially true for chemical releases that produce a vapour hazard downwind of the contaminated area.
3.4.3 Stability and persistence of the substance. The recovery strategy will depend upon the persistence of the substance in the environment (see Box 3). Although chemical and biological substances vary considerably in their properties and in their effects on humans, substances are not always persistent for long periods of time and may safely break down over a few days when exposed to rain or sunlight or can be destroyed by using simple treatment processes such as spraying with dilute bleaching solutions. However most radiological substances, and some chemical or biological substances, are highly persistent. Additionally CBRN substances may penetrate into cracks and crevices or be absorbed into materials such as rubber and paint. If this occurs they will be protected from the decontamination process and so could later be released, giving rise to a persistent contact or vapour hazard to members of the public.
3.4.4 Nature of the location. Decontamination techniques for urban clean up in towns and cities will be different to rural clean up in the countryside. The clean up of substances released in the open environment will be different to clean up inside a structure. Natural weathering and wet decontamination techniques will be most effective for chemical and biological incidents which take place outdoors either in urban or rural environments.
3.4.5 Effectiveness of recovery options. Recovery decisions should take account both of the expected benefits of different decontamination options and also their likely contribution to an early return to normal living within the affected population. NRPB has developed a simple categorisation scheme for comparing different recovery options for radiological incidents, based upon the likely scale, duration and resource requirement necessary to implement each option(19).
Potential recovery options may be broadly divided into three categories; those that are moderately dose-reducing, incur relatively little disruption or require few resources, and which can be completed soon after the incident (Category A); those that are more strongly dose-reducing but which incur significant disruption or require significant resources, or can only be carried out over protracted periods (Category B); and those that are either poorly dose-reducing or only moderately dose-reducing and incur significant disruption or require significant resources (Category C). The CBRN recovery strategy should focus initially on Category A and Category B options, although the local authority may still wish to implement Category C options for reasons other than health protection, for example public reassurance. There may also be a role for cost-benefit analysis in decision-making, for example when it may be more cost-effective to resurface a public highway rather than remove very low levels of persistent contamination.
3.4.6 Health and safety management. Risks to the health and safety of people will need to be managed as an integral part of the recovery strategy. This will include local authority staff, clean-up contractors, sewerage company workers, the Police and Fire Services, external advisors, possibly voluntary organisation workers and members of the civic community, who may potentially be exposed to residual levels of CBRN substances during different phases of the clean-up operation. The general approach to controlling exposure to hazardous substances is explained on the Health and Safety Executive's (HSE) COSHH Essentials web site(20,21).
HSE's principles of hazard control involve the following steps; assess the risks to health arising from potential exposure to a CBRN substance (Step1); decide what precautions are needed (Step 2); prevent or adequately control exposure (Step 3); ensure that control measures are used and maintained (Step 4); monitor the exposure of people (Step 5); carry out appropriate health surveillance (Step 6); and ensure that people are properly informed, trained and supervised (Step 7). Each of these steps will need to be considered within the local authority's recovery strategy.
Box 3: Persistence of CBRN Substances
The persistence of a CBRN substance is its ability to remain hazardous in the environment over time. The choice of recovery strategy will be strongly influenced by the persistence of the substance being cleared up. Substances with low persistence such as sarin or cyanide disappear within hours. A persistent chemical substance might last several months or even a few years under the right conditions. For chemical and biological substances the actual rate of deterioration will partly depend on local weather conditions. For example chemical substances evaporate faster on hot days than cold days and biological substances break down faster in direct sunlight than in the shade. A persistent radiological substance may take many decades to completely breakdown and the rate of decay is not affected by external factors such as the weather.
3.5 Priority actions for recovery
3.5.1 Stabilise any further migration of contamination. A physical cordon should be established around the suspected perimeter of contamination to restrict entry and exit. However because most types of CBRN release result in 'splatter' - small areas of contamination in a largely uncontaminated environment - it may not be possible to establish a precise boundary between uncontaminated and contaminated areas. Local authorities should use their judgement after seeking advice from specialist agencies to decide an appropriate hazard management zone (which will be larger than the suspected contaminated perimeter). The hazard management zone should be physically sealed off as far as possible, e.g. with plywood board similar to that used on construction sites. Where possible contaminated water should be intercepted in storage tanks for treatment and safe disposal. In the open environment, CBRN contamination in watercourses may need to be temporarily blocked and the path of the watercourse diverted. Containment of any affected livestock, cats and dogs, and feral animals may also need to be considered to prevent the spread of infectious substances.
3.5.2 Survey the affected area. Environmental monitoring to map affected areas after a CBRN incident would provide the main basis for decision-making on the decontamination and restoration of the environment to as near as normal use as practicable. The sampling strategy should focus initially on confirming the safety of the cordon perimeter. However it may not be necessary to carry out detailed surveys of the hazard zone, until after initial decontamination has been carried out. This is partly because in cases where the release of CBRN substances comes from improvised terrorist devices their relatively inefficient or incomplete nature may minimise the area contaminated. If terrorists used a greater quantity of material, the most likely effect would be higher levels of contamination close to the release site rather than a proportionate increase in the area affected. Depending on the specific CBRN substance involved, a survey of the hazard area may be practicable.
3.5.3 Decide target clearance levels. The recovery strategy will be influenced by knowledge of the risks to public health from the substance, what level of residual contamination may safely be permitted to remain ('safe clearance levels') and the availability of suitable detection technologies capable of monitoring and distinguishing between levels of residual contamination above and below the agreed safe level. These technologies and standards are well understood for radiological substances. However there remain a number of technical uncertainties when applying military decontamination data to civilian clean-up scenarios. There is a wide range of potential chemical or biological weapon substances for which no safe clearance levels have been firmly established for civilian application. In the absence of clearance level data, experts from Dstl Porton Down will provide advice to local authorities. In addition two handbooks dealing with recovery from CBRN incidents are being developed by Defra for local authority use. The handbooks compile the best available safety data, principally from experience of past accidents and from defence sources, and give practical advice on the management processes and methods of recovery from CBRN incidents, supported by relevant technical and logistical information and decision-aiding flowcharts.
3.5.4 Develop phased recovery options. The process of remediation may require a phased approach with different remedial actions being carried out in sequence (see Box 2). Remediation is likely to follow a progression from impact assessment, through to successive treatment actions and then monitoring to confirm successful clean up. When deciding between different options the questions, which local authority managers must address, are similar to those which would apply to any pollution prevention and control strategy(22).
(a) How effective will the recovery option be?
(b) Is the recovery option environmentally acceptable?
(c) What clearance level will adequately protect public health?
(d) What levels of residual contamination will be acceptable?
(e) How will the authority establish public confidence in its clean-up strategy?
(f) How quickly can the option be implemented?
(g) What resources will be required?
(h) What wastes will be generated?
(i) How will they be managed and disposed of?
(j) What are the environmental impacts of the disposal options?
3.5.5 Transport and disposal of wastes. Waste management planning is an integral component of the recovery strategy. CBRN recovery techniques may involve demolishing highly contaminated structures, pressure washing lightly contaminated surfaces, sandblasting harder surfaces, replacing road surfaces and sweeping and vacuuming streets. This will produce large volumes of contaminated aqueous slurries and solid rubble. Early intervention actions by the emergency services will also generate wastes, mainly large volumes of contaminated water and bags of contaminated clothing from mass decontamination of the public. Introduction of statutory restrictions on foods from an affected area may also result in large volumes of waste crops and farm produce, including milk. The success of the recovery option may depend upon the availability of disposal routes for these wastes and also the receiving capacity of the disposal locations.
The Water UK Protocol for the Disposal of Contaminated Water(23) provides useful guidance on dealing with incidents involving CBRN contamination of water and the disposal of waste water resulting from decontamination work etc. For solid wastes the local authority may need to consider an interim management strategy - such as temporary storage of hazardous wastes in ISO containers at a military site or a sports stadium - to allow the operators of disposal facilities sufficient time to safely receive, store, treat and dispose of the wastes. The local authority may also need to consult the local community, regarding the temporary storage, transport routes and intended disposal locations of CBRN wastes to maintain public confidence.
(18) Two technical handbooks dealing with recovery from CBRN incidents are being developed mainly for local authority use. The handbooks will give practical advice on the management processes and methods of recovery from CBRN incidents, supported by relevant technical and logistics information and decision-aiding flowcharts.
(19) See Intervention for Recovery After Accidents. Documents of the HPA Radiation Protection Division. Volume 8. No 1. 1997. Available from the HPA web site http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1153846673595?p=1153846673595 [External website]
(20) Legal requirements are set out in the Control of Substances Hazardous to Health (COSHH) Regulations 2002.
(21)COSHH Essentials is a free on-line risk assessment service for hazardous substances, provided by HSE at http://www.coshh-essentials.org.uk/ [External website]. The key principles of hazard control are explained at www.coshh-essentials.org.uk/assets/live/indg136.pdf [External PDF]
(22) For example, the European system of Integrated Pollution Prevention and Control (IPPC) includes formal licensing requirements to plan ahead for eventual decommissioning of Installations and to restore sites to their former condition. For further information see the site report requirements under IPPC, discussed in 'Integrated Pollution Prevention and Control: A Practical Guide' published August 2000 by DETR. http://www.defra.gov.uk/environment/ppc/ippcguide/index.htm. [External website]
(23) 'Protocol for the Disposal of Contaminated Water'. Water UK. Second Edition. April 2003 obtainable via local water undertaking.
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