Depending on the nature of the chemical incident, facilities such as manufacturing plants, agricultural facilities, transit systems, and/or other commercial or public entities may be closed to prevent exposure and reduce the distribution of contaminated materials. Facility closures are important when work is being done to control a crime scene or prevent evidence removal, destruction, or decontamination.
If health effects are immediate, patrons and employees evacuated from impacted facilities/venues will need to be triaged and treated (see also KPF 6, Augment Provision of Health and Medical Services to the Affected Population), and if necessary, interviewed by law enforcement officials. This interview process may be instrumental in the identification of previously unknown contaminated areas, prevention of secondary attacks, and/or the immediate capture of the perpetrator(s). Nearby, non-impacted facility/venue evacuations can be handled similarly to bomb threats or other police actions.
If health effects are delayed (and the incident is not otherwise recognized), exposed individuals likely will disperse throughout the city, region, state, country, and even internationally, which will likely result in people becoming symptomatic at locations far removed from the release site. This movement of survivors could complicate the identification of the incident location and the chemical involved and could result in ongoing exposures.
Water systems. Utility level water sources often can shut off their systems, or portions thereof, immediately after notification of a problem to help contain the spread of contamination. In fact, “do not use” (DNU) order notices and alternate water supplies are a core part of local emergency planning in most areas of the U.S., allowing for the protection of public safety while characterizing the extent of a chemical release threat. As discussed in the Prologue, a DNU was put in place around Charleston, WV, to protect the public when the water system there was contaminated by a leaked chemical.4
Indoor public venues.64 In most situations, measures should be taken to contain a release within an indoor public venue by shutting down ventilation systems, because:
- Venting moves contamination into the surrounding streets. While ventilation removes contamination from the venue itself, it transfers the contamination to the streets nearby, potentially exposing more people to the hazard. Even with a ventilation shutdown, responders should expect some residual contamination spread.
- Venting moves contamination through the venue. By pulling contaminated air throughout the venue, more individuals could be exposed.
- “Late” in the event, venting has limited effectiveness in reducing exposures. For many scenarios, by the time an incident is identified, most onsite exposures have already occurred. If the venue is closed and unexposed patrons are prevented from entering contaminated areas, ventilation will provide limited benefit.
Transit (subway) systems.64 The consequences of a chemical release within a transit system may be widespread. Contamination spreads quickly in a subway system as trains move through contaminated station(s). Every train passing through the area acts as a moving source as it continues, such that several stations can become affected within minutes of release. Train and passenger motion can also spread contamination between subway lines at crossover stations. In fact, unless it is shutdown early in the event, the system will efficiently spread contamination and exposed individuals throughout the city; responders should expect impacts at many, widely separated stations. For example, the delayed shutdown of the Tokyo subway during the 1995 sarin gas attack resulted in the contamination of hundreds of people and fifteen stations along multiple train lines.
Since the amount of time any single passenger spends in a subway transit system is often relatively short (15-60 min), many exposures can be avoided by preventing people from entering the system altogether, or even by preventing a single train from entering a contaminated area. In fact, subway events should trigger a system-wide shut-down, including evacuating all patrons and stopping all trains. After system evacuation, station(s) must be secured to protect unaware individuals from entering the hazard area and becoming exposed and/or contaminated.
For the same reasons as with other high-traffic indoor public venues, shutting off active ventilation following a chemical release in subway systems is recommended. Such action helps to avoid spreading contamination further throughout the system and into the streets above, thus containing the substance and helping to prevent additional exposures. Exceptions to this can be made in some situations; for example, the Tokyo subway system’s powerful air exchange system is credited with helping to reduce the number of casualties caused by the 1995 sarin gas attack.65
Usually, transit system contamination should trigger a shut-down of ventilation systems to prevent contamination of above-ground areas. However, venting can be a powerful mitigation tool when the release is rapidly recognized and known to be small, and/or venting can be done with minimal above-ground exposures. This tool should only be applied to a subset of scenarios identified through detailed planning and coupled with an active, real-time field detection system and a thorough playbook of ventilation options.
If contamination of a subway system is suspected in a jurisdiction lacking established sheltering procedures, the community should consider sheltering above-ground populations within ½ mile of stations suspected of significant contamination.
Footnotes
4. CSB. (2017, May). Chemical Spill Contaminates Public Water Supply in Charleston, West Virginia. Report Number: 2014-01-I-WV.
64. Canadian Security Intelligence Service. (1995, August). Commentary No. 60: The Threat of Chemical/Biological Terrorism.
65. Centers for Disease Control and Prevention. (2003). Nicotine poisoning after ingestion of contaminated ground beef – Michigan, 2003. Morbidity and mortality weekly report (MMWR). 52(18), 413–416.