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Radiological Contamination Control

"Module 8"

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

8.00 Overview

This module examines the control measures necessary to prevent the spread of radiological contamination following detonation of a dirty bomb. This module considers entrainment of contamination to station areas. Explosive devices internally are considered in module 3.

8.01 Typical incident

A small explosive device with limited destructive potential is expected as the vector agent for distribution of contamination. In this outline, the explosion is considered externally of the station specifically and internal explosions are considered separately in module 3.

8.02 Health Hazard

All radiation in it’s various forms is a health hazard, the proximity and dose to humans is the relevant factor in hazard assessment. Inhalation of radioactive particulate is in this particular event likely to result in lung cancer and little prophylactic care is possible, therefore prevention is essential if possible.

8.03 Hazard and Risk

Respiritable radioactive fallout of particulate matter is expected in the region of <15 micron. The fallout contamination in it’s various sizes is expected to remain airborne for some time due to both Brownian motion and transportation by air movement. Natural air movement will, where air speed is in excess of 5 mph dissipate the contamination and it is therefore essential to control and localise the particulate where possible.

This will result in a continuous risk to persons exposed. Secondary contamination vectors include the transportation by persons evacuating the hot zone from contaminated clothing. Risk reduction therefore depends on both personal decontamination and environmental control factors.

8.04 Objective

Particulate matter will eventually settle and fall naturally, however it’s re launch must be prevented. Where particulates are airborne they must where possible be encouraged to fall to prevent inhalation. Radioactive particulate is readily identified by electronic counters but decontamination would be a long and laborious procedure and therefore control is essential to allow for planned action within acceptable time frames.

8.05 External Protocol

a. external operations

It is imperative that airborne contamination is brought down as quickly as possible. Rain may be a simple measure and the RAF may be required to instigate precipitation by cloud seeding to the upper atmosphere.

This would effectively wash the air. Falling radioactive particulate may therefore be washed into local drains which may be controlled by the waste water authority. This is seen as a trade off as drain contamination is preferable to human effects and is a problem which would materialise in any event.

Following this initial measure the streets and lower buildings must be washed by fire hoses.

The removal of all contamination is impossible and therefore containment is required to prevent re release of particulate following drying and air movement.

b. external controls

Low pressure spray of a temporary lock down solution must be applied to all surfaces to encapsulate particulate. This solution must enable both effective lock in but be readily removable to enable future decontamination procedures. Liquid, water borne PVA should be introduced into the fire hose following the initial washing down. Application should ideally be from above and the use of building dry and wet risers in the locale should be considered with application through windows and roof access.

8.06 Station Internal protocol

Overview

Two types of control are envisaged either immediate or delayed, this may be dictated by the severity of the incident. Components of the assessment include passenger presence (c.) or post evacuation (d.) section 8.07.

Passenger transience

While the safety of passengers is paramount the reality is that without respiratory protection they may have already been exposed to inhaleable radiological particulate and therefore may be later casualties. Clearly there is need for passengers to be equipped with disposable particulate masks, issued prior to the event, (location) either by train or station staff. Where this is considered un-acceptable for various reasons, substitute action must be considered either to reduce exposure or contamination spread.

8.07 Controls

c. As passengers evacuating an incident are unlikely to be controllable, limitation to exposure must be provided where possible. This can be accomplished by the use of wet fogging techniques to reduce the air loading of particulates. (see modules 12 –13)

d. The application of a water or solvent based encapsulate which will continue to attract and trap particulate. This can be enhanced by the use of ionisation equipment which at low cost could be installed either pre or post incident. Air borne contamination reduction can also be increased with the use of Heppa or other air scrubbing techniques as previously described in other modules.

8.08 Conclusion

The release of a dirty bomb would represent a significant health hazard from inhalation over a large area and for a long duration. The immediate and substantial response from the unified action of all possible sources must be considered to prevent the spread of contamination. Typically airborne contamination may travel hundreds of miles although possibly limited by content. Radioactive contamination is relatively easy to identify for decontamination purposes, the significant potential must be limited by urgent lock down and encapsulation procedures. This will provide limitation of the contaminated area and enable planned, controlled decontamination.
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