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Biological Protective Measures

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Federal Emergency Management Agency (FEMA)

The Federal Emergency Management Agency - a former independent agency that became part of the new Department of Homeland Security in March 2003 - is tasked with responding to, planning for, recovering from and mitigating against disasters.

This chapter is based on guidance from the CDC/NIOSH and the DoD and presents protective measures and actions to safeguard the occupants of a building from CBR threats.

... The dip between 0.1 and 0.3 microns represents the most penetrating particle size. Many bacteria and viruses fall into this size range. Fortunately, microbes in this range are also vulnerable to ultraviolet radiation. For this reason, many health care facilities couple particulate air filters with ultraviolet germicidal irradiation (UVGI)...

Ultraviolet Germicidal Irradiation (UVGI) has long been used in laboratories and health care facilities. Ultraviolet radiation in the range of 2,250-3,020 Angstroms is lethal to microorganisms. All viruses and almost all bacteria (excluding spores) are vulnerable to moderate levels of UVGI exposure. Spores, which are larger and more resistant to UVGI than most bacteria, can be effectively removed through high efficiency air filtration. For these reasons, today most UGVI systems are installed in conjunction with high efficiency filtration systems in many health care facilities.

Ultraviolet (UV) lamps resemble ordinary fluorescent lamps (see Figure 5-10), but are specially designed to emit germicidal UV and include a glass envelope to filter out harmful, ozone forming radiation. The lamps are available in a variety of sizes and shapes and must be mounted in special housings and located so that people are not exposed to direct irradiation. Newer more advanced compact UV tubes provide higher output in the UV-C bandwidth (253.7 nanometer wavelength) and increased reliability.

UVGI safety measures, such as duct access interlocks that turn off the lamps when the duct housing is opened, should be used.

Manufacturers offer UVGI systems suitable for in-duct or large plenum installations. Retrofitting UVGI systems can also be relatively simple if sufficient space is available. There are UV lamps that can be mounted externally in ductwork and pressure losses across such lamps are often negligible. When installing a UVGI system, attention must be paid to maintaining design air velocity and temperature of the UV lamps. Cooling the plasma inside a UV lamp can significantly affect its UV output. Polished aluminum reflective panels can also be used to increase the intensity of a UVGI field in an enclosed duct or chamber. The design velocity for a typical UVGI unit is similar to that of particulate filters (about 400 feet per minute). It is very important to properly
design and install UVGI systems in order to obtain the desired effects. Improper systems may provide a false sense of protection. For a discussion of the factors that should be considered when designing and sizing a UVGI system, additional information can be found in W. J. Kowalski, Immune Building Systems Technology (McGraw Hill, 2003).

A design utilizing a combination of filtration and UVGI can be very effective against biological agents. Smaller microbes, which are difficult to filter out, tend to be more susceptible to UVGI; while larger microbes, such as spores, which are more resistant to UVGI, tend to be easier to filter out.


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