Ask A Scientist Chemistry Archive

name        Jackie
status      educator
age         50s

Question -   In a recent response about UV, Vince Calder stated that
Germicidal UV-C lamps produce ozone. How much and how is this measured?
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UV-C lamps pose two potential risks, one from UV radiation; the other from
ozone generation:
1. Ultraviolet radiation ~254 nm is extremely damaging to all biological
tissues. It is this fact that makes UV-C lamps biocidal. Corneal tissue is
especially sensitive to UV-C (as is UV-B) radiation, hence the lamps must
be shielded and located to isolate their radiation output from direct
exposure to human tissue. This presents design dilemma. If physically
isolated, diffusion or unforced convection the mode of contact between the
lamp and pathogens, the process is extremely inefficient, because diffusion
simple convection are slow processes. In addition, dust and suspended
aerosols accumulate on the surface of the lamps and reflectors rapidly
reducing their UV-C output. If pathogen laden unfiltered air is pumped or
blown past the lamps, contact time is reduced and suspended particles of
dust, aerosols, and organisms collect on the lamps and reflectors even more
quickly. It is for this reason that (in a laboratory environment) UV-C
lamps are purged with the dust-free effluent gas from liquid nitrogen, or
filtered argon, to protect the lamp and reflectors.
2. UV-C lamps typically produce ozone, O3. By any measure ozone is
extremely toxic -- one of the most toxic substances known, surpassed only
by F2 as an oxidant. The lungs are the principle pathway into the body.
Ozone is so toxic that it has no systemic toxicity because it cannot cross
the fluid layer in the lungs before it reacts [1]. Both ozone itself and
its oxidation products of reaction with lung lining fluids are respiratory
irritants [2-3]. The latter producing longer lived irritants.
The toxicity of chemical substances is measured by several indeces,
depending upon the mode and time of exposure. For ozone, these are [4]:
NIOSH REL = 0.1ppm; OSHA PEL = 0.1ppm; ACGIH TLV = 0.1ppm; IDHL= 5ppm.
Compared to highly toxic H2S [5]:
= 10ppm ; = 20ppm; = 10ppm = 100ppm
Ozone is 20 to 100 times more toxic than hydrogen sulfide, depending upon
the exposure index selected.
False and unsupported claims for the benefits of ozone have led to a number
of "cease and desist" or "consent" orders by the Federal Trade Commission
[6], [7].
In summary: The extreme toxicity and health hazards of ozone are thoroughly
documented in the both government and peer-reviewed literature. It has not
been shown to be safe and effective as an air purifier except at
unacceptably high concentration.
If Dustfree, Inc. has products that produce high intensity UV-C radiation
without concomitant production of ozone, they should certainly provide
their customers with independent third party evidence of the safety and
efficacy of their systems, because that would certainly be a technological
breakthrough in atmospheric photochemistry. In the absence of such evidence
I stand by my many years experience safely handling UV-C radiation: UV-C
radiation produces ozone.

[1] "Mechanisms of Ozone Toxicity" Carol Soo, thesis, Univ. of Cincinnati,
2002
[2] Lippmann M., "Health Effets of Ozone: A Critical Review", J. Air
Pollution Control Assoc., 39, 672-695
[3] http://www.cal-iaq.org/o3_fact.htm (and 19 literature citations therein)
[4] http://www.cdc.gov/niosh/idlh/10028156.htm
[5] http://www.cdc.gov/niosh/npg/npgd0337.htm
[6] http://www.ftc.gov/opa/2000/01/alpine2.htm
[7] http://www.ftc.gov/opa/1995/09/quantum.htm

Vince Calder
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The truth of the matter is that UVC radiation below 240 nm can form
ozone.  Above that, you're fine.  You've got from 240 to 315 nm of UVC
that is not ozone producing.  At least, that's that the Navy thinks:

http://www-nehc.med.navy.mil/downloads/ih/uvdoc2.doc

I'll bet that some smart person has figured out a way to block lambdas
below 240nm without attenuating the rest of the UVC range too much.

David Hiers
Systems Engineer
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