Positive-pressure filtration systems draw contaminated air into the building through special filters that remove the contaminants. This creates a slight positive pressure in the building, which in turn prevents the nonfiltered, contaminated air from leaking into the building. Experience suggests that such systems, however, are expensive and difficult to properly engineer. A less expensive but less protective measure is to engineer the building controls so that the HVAC system could be completely shut down. Little outside air would be drawn into the structure if all doors and windows were closed.

The ability of an action to adequately protect people in a healthcare facility depends on the characteristics of the toxic agent(s) involved, the size and nature of the release, meteorological conditions, the characteristics of the population affected, and the ability of the threatened structures to provide protection from outdoor agent concentrations. Deciding to shelter-in-place requires a prediction of the outdoor plume concentration of the toxic agent that will occur in the risk area, an estimation of the concentration that will occur inside the buildings at risk, and a calculation of the indoor estimated level of exposure. Deciding to evacuate requires an estimation of how long it will take to move patients and staff out of the building and when they will reach a safe distance compared to the outside concentration that people will experience while evacuating; that is, calculating exposures to those who evacuate in the plume will be considered against exposures to those who have not left (Sorensen, Shumpert, and Vogt 2002).

The indoor concentration of a contaminant is determined by infiltration rates into a building and the inside circulation of air. The inside environment will have a lower peak concentration of a contaminant than the outside air. The lower the air exchange, the lower the peak concentration. Infiltration is measured by air changes per hour (acph) between the outside and the inside or the number of times each hour that an enclosure’s total volume of air is exchanged with outside air. An average air exchange rate for office buildings is estimated to be 0.66 acph and an industrial building to be 0.31 acph with the HVAC system(s) off and doors and windows closed (Engelmann 1990). Little is known about the movement of contaminants inside buildings, especially large and complex structures such as hospitals.

Overall exposure to contaminants in a closed indoor environment will be similar to the overall outdoor exposure because contaminants remain in the building after the plume has passed. If reducing total exposure is the goal, as opposed to reducing peak concentration, then the facility needs to be evacuated or ventilated after the plume has passed or the outdoor concentration is less than the indoor concentration (Rogers et al. 1990).

Sheltering for a biological hazard is slightly different from that for a chemical vapor in that hospital HVAC systems are designed to filter out most aerosols in the size range of biological agents (0.5 to 10 microns) (Weik and Weik 2001). Thus, leaving the HVAC system on would be warranted if the hospital is not under positive pressure.

Sheltering for a radiological hazard is somewhat different from that for chemical hazards in that a building will provide some protection against radiation from inhalation exposure as well as exposure from atmospheric clouds and ground deposition. The amount of protection against radiation is determined by the type of structure and location in the structure. Interior rooms and basements in buildings such as hospitals would typically reduce exposure from a cloud source by 70 percent to 90 percent and from a ground source by 98 percent to 99 percent (Schleien 1983).


The National Research Council (NRC 1999) defines decontamination as the process of removing or neutralizing a hazard from the environment, property, or life form. However, no consensus nationally or among agencies has been reached on standard operating definitions of decontamination, and existing procedures may contradict best healthcare practices for protecting potentially exposed victims as well as healthcare providers.

For decontamination to be effective, the following three elements must be in place:

  1. The contaminants are correctly identified.

  2. The procedures and equipment are available and properly employed to neutralize (or remove) the contaminant.

  3. The reduction of risk is defensible by scientific or regulatory standards (which is not always possible).

Furthermore, most current decontamination systems are labor intensive and require excessive quantities of water. As Macintyre et al. (2000) note, most decontamination guidelines for treatment of exposed victims were created following military models and are inappropriate in today’s civilian healthcare settings.

This discussion is not intended as an all-inclusive treatment on decontamination dos and don’ts but is meant to alert managers to the potential difficulties and pitfalls in planning procedures for decontaminating victims exposed to hazardous substances.

Types of Decontamination

To protect the healthcare facility, it is important to understand where and how (or if) decontamination is performed outside the medical facility, because the problems associated with decontamination of victims (including secondary contamination) in the ED can often be attributed directly to those factors. The degree to which a patient is decontaminated in the prehospital setting depends on the medical decontamination plan, available resources and medically trained personnel, the weather, and characteristics of the contaminant.

General protocols suggest that patients exposed to a hazardous chemical or biological substance should receive, at a minimum, gross decontamination before transport and treatment. Gross decontamination involves showering clothed patients with copious amounts of water, often conducted by a HAZMAT team with a fire hose or by having victims move through a HAZMAT decon tent or other treatment facility. Patients requiring additional medical attention, antidotes, or other emergency care should receive that care depending on the substance’s effects and the ability of staff to protect themselves during treatment. For some situations, such as a patient exposed to a radiological or nonvolatile chemical substance, use of barrier nursing clothing is ample protection. However, if the chemical is highly volatile or persistent, staff should never attempt care or bring potentially contaminated patients into the hospital without appropriate respiratory protection. This includes admitting patients to ED waiting areas where the possibility of secondary contamination could shut down operations.

Hazardous-materials teams traditionally handle decontamination of the environment and persons exposed to hazardous substances, generally relying on a conservative model that advocates precautionary decontamination of potentially exposed victims. The HAZMAT definition of medical decon or patient decon is what most healthcare providers would consider gross decontamination. The procedures, however, are not much different from those proscribed in hospital settings. The first step is removal and disposal (i.e., bagging and sealing) of patients’ clothing and personal belongings. (Cox [1994] estimates that this simple process removes 70 percent to 80 percent of the contaminant, but little scientific data support that assertion.) Victims are then given a quick overall rinse with water.

Secondary decontamination involves washing rapidly with a decontamination solution—usually a diluted bleach or soap and water—and rinsing again. At this point, victims can be dried, given clean clothes, and sent home or transported to a medical facility. The degree of proficiency will vary depending on equipment, resources, and training. One problem is providing privacy to victims, as not all HAZMAT teams are equipped with individual decontamination units or trailers.

Alternatively, mass decontamination processes victims in one or more groups. Chemical warfare agents can cause large numbers of casualties if dispersed in a vapor or aerosol, as manifested in the sarin incident in the Tokyo subway. Such a situation could also occur in a high-profile event at a stadium, a concert, or an airport. The process requires cordoning off several exits where a decontamination corridor can be set up with fire department aerials and/or deluge guns in close proximity. The nozzles are set at low volume so as not to inflict damage but to maximize the amount of water to which each victim is exposed. Ambulatory victims progress through the deluge so that they may be grossly decontaminated. In conjunction with removal of clothing, this will likely suffice to decontaminate those victims not exhibiting signs or symptoms of chemical agent exposure.

A second method is to set up a sprinkler head near the exit point as a rudimentary decontamination shower. In this scenario, water delivered at 500 gallons per minute will produce 8 gallons per second. If the victim remains in the shower for 3 seconds on average, he or she is exposed to 12 gallons, or the amount used in a normal shower.

In either scenario some clothing is left on, which reduces the effectiveness if vapor has penetrated to the skin. Also at issue is the runoff of wastewater with possible contaminants, the disposal of which must comply with local or state environmental regulations.

Self- and buddy-decontamination techniques can also be employed by first responders, workers in hazardous situations, and groups trained in self-help for emergencies. Such techniques may be needed in situations in which immediate removal of contaminants is essential and no time is available to set up a decontamination operation.

Water temperature is a comfort issue that can affect the time spent showering. Normal fire hydrant water temperature is 55 to 65 degrees Fahrenheit. Discomfort during showering is a particular issue with children and the elderly who may suffer additional distress, especially if the ambient air temperature is much cooler or the weather is windy and cloudy. The outside decontamination process is more traumatic than that conducted in an enclosed environment, especially if victims feel a lack of privacy during the process.

Popular Posts