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
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