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Ozone is
a toxic gas, and like chlorine can cause severe illness and even death
if inhaled in sufficient quantity. However, ozone systems have certain
safety advantages that can be incorporated in water bottling plants and
are not available with the chlorine disinfection process.
Ozone is generated
onsite, eliminating transportation and storage and handling hazards. Also,
the generation system can be shut down if an ozone leak develops. Another
safety advantage is the physical characteristic of ozone that allows it
to be detected (smelled) at concentrations much lower than harmful levels.
In addition
to safety precautions against exposure to ozone, protection against noise
and electrical hazards should be built into the design and operation of
an ozone disinfection system.
Recommended
exposure limit to ozone
A study of
the health effects of ozone exposure was conducted by the US Air Force.
Another summary of ozone's health effects was compiled by the American Society
for Testing and Materials (ASTM) in support of its recommended standard
for limiting human exposure to ozone. The reported biological effects range
from dryness of mouth and throat, coughing, headache, and chest restrictions
at concentrations near the recommended limit, to more acute problems at
higher levels.
Recommended
ambient ozone exposure levels have been proposed by the Occupational Safety
and Health Administration (OSHA), the ASTM, the American National Standards
Institute (ANSI), the American Conference of Governmental Industrial Hygienists
(ACGIH), and the American Industrial Hygiene Association (AIHA). Recommendations
are as follows:
· Control
occupational exposure. This is so workers will not be exposed to ozone
concentrations in excess of a time-weighted average of 0.2 milligrams per
cubic meters (mg/m3) — 0.1 part per million (ppm) by volume —
for eight hours or more per workday. Workers should not be exposed to a
ceiling concentration of ozone in excess of 0.6 mg/m3 (0.3
ppm by volume) for more than 10 minutes.
These recommended
limits for ozone concentration are much higher than the concentrations at
which ozone can typically be smelled. Generally, an individual can detect
ozone at concentrations ranging from 0.02 to 0.1 mg/m3 (0.01
to 0.05 ppm by volume). The more often a person is exposed to ozone the
higher the required concentration for detection.
· Provide
ambient ozone concentration monitors. The subject of safety in the design
and operation of an ozone system should receive a high priority. All ozone
systems should be provided with an ambient ozone monitor or monitors that
measure the ozone concentration at potential ozone-contaminated locations
in the plant (e.g., at various places in the room housing the ozone generators
and where workers are potentially exposed to ozone off gas).
A single monitor
may be installed and the air from different locations pumped to the monitor
for detection of ozone concentration. The monitors should be set up to sound
an audible and visual alarm when the ozone concentration reaches 0.2 milligrams
per liter (mg/l) (0.1 ppm by volume), and should be set up to shut down
the ozone system when the concentration exceeds 0.6 mg/l (0.3 ppm by volume).
However, if
the ozone equipment is located in an area where smoggy days due to ozone
levels in the atmosphere are common, higher values may be necessary to prevent
false alarms generated by ozone levels in the atmosphere not due to detected
ozone leakage by the ozone generation system.
A listing
of reliable ozone monitors used for ambient monitoring purposes may be obtained
from ozone generation equipment manufacturers. These monitors are factory
set and can be checked and calibrated using extensive calibration procedures,
but loss of calibration typically has not been a problem.
Under normal
operating conditions the monitor does not "alarm" and the operators cannot
smell ozone. Therefore, on a periodic basis operators should check the operation
of the monitor by directing a small volume of ozone from the generator to
the monitor to test the meter's responsiveness. In this manner the operators
can be assured that the monitor will respond in case of an ozone leak.
Gabe Ergler
is an applications specialist for O3 Water Systems, LLC, in Snohomish, WA. |