A Solution to Chemical Threats and the Vulnerabilities of Subway Systems

DRY DECONTAMINATION

Subway systems were created to relieve traffic congestion and reduce air pollution, problems caused an enormous increase of cars and buses due to rapid urban development. Today, it has become the main means of transportation in big cities, for citizens and metropolitan area residents. Large urban railway networks have multiple lines, extending over hundreds of kilometers and stations. The average number of passengers per day can amount to millions[1].

CBRN attacks on public transport systems have catastrophic consequences, as clearly shown by the Tokyo subway attack in 1995.

This threat has also been recognised by the International Association for Public Transport (French: Union Internationale des Transports Publics, UITP)[2].

One of the most important challenges facing those responsible for the safety of these transit systems, therefore, is to protect the daily passengers against chemical incidents. The two principal categories of chemical weapons or devices typically used by terrorists are chemical warfare agents (CWAs) and toxic industrial chemicals (TICs).

Enclosed spaces such as subway systems are particularly susceptible to attacks using CWAs and TICs.

The airflow traveling through subway tunnels can rapidly disperse chemicals from their source of release toward unsuspecting passengers – those already aboard the train as well as those waiting in the station and even outside, at street level. Research in the subway system of a European capital have confirmed this thesis.

The attack in Tokyo in March 1995 was used as a reference for an experiment carried out jointly with a subway operator of a European capital; 12 people were killed in this Tokyo attack and several thousand were injured. The gas used was sarin, a military nerve agent. The method, quantity and location of application were adopted by the author for the experiment in the subway of this European capital.

The simulation experiment was carried out in a train set provided by the subway operator and in two subway stations); these two stations were chosen because they are connected by a straight tunnel with no difference in height, which also corresponds approximately to the average distance between stations of this subway network. 

In the experiment carried out as part of this research, an industrial, inert (non-hazardous) gas was used to simulate an attack with warfare agents and the resulting consequences. The amount of gas emitted corresponded to the vaporizing amount of warfare agent of 40g/hour at 20˚C.

This involved taking more than 115 air samples at various points in a subway train set and in two subway stations and analyzing the results quantitatively to obtain concentration values, which in turn made it possible to determine the expected number of victims and thus the potential threat of such an attack.

Overall, the following number (& percentage) of people affected by the vaporizing agent through primary exposure can be assumed for an attack scenario (in train and on platform), with maximum occupancy of the affected train and a platform of the station, 982 people:

• 668 (68%) intoxicated, but can leave themselves
• 240 (24%) intoxicated, need to be rescued
• 74 (8%) fatalities.

Passengers are also faced with typically limited egress from many stations, and this hampers a rapid evacuation; all of this makes emergency decontamination an essential tool, as it allows for immediate live-saving measures.

It is of utmost importance to establish easily accessible emergency decontamination systems to save lives, as seen by the numbers above. These systems should be easy to use, and preferably should be capable of performing emergency decontamination against liquid and vapor chemical threats. Dry decontamination should be used as the default intervention for anyone that is suspected of being contaminated.

Dry decontamination should consist of a formulation of non-toxic high-performance specialty materials effective at neutralizing a wide range of toxic chemicals with the added capability to destroy chemical warfare agents. Furthermore, it should be non-flammable, non-corrosive, and significantly reduce both liquid and vapor hazards. The dry powder should neutralize threats upon contact, therefore on-site incident management and clean up times are reduced.

FAST-ACT addresses both liquid and vapor hazards. FAST-ACT can be safely applied to any liquid spill or vapor release enabling Emergency Responders to utilize one technology when faced with a wide variety of known or unknown chemical hazards.

Field trials with GB (sarin) have demonstrated that GB vapours can be removed almost instantaneously, below the detection capabilities of handheld instruments.

Very recent research (2023) and testing have shown that FAST-ACT, dispersed from pressurized cylinders, demonstrated to be an effective dry active decontaminant against VX and HD percutaneous challenges.