Getting Technical
CHARLES NICOLSON
Charles Nicolson has a physics and chemistry degree from Natal University which he subsequently put to good use by applying speciality chemicals in mining and industrial processes where water is a major factor . This created an enduring interest in water technology , a passion that expanded to the HVAC industry in 1984 when he joined BHT Water Treatment . Since then , water technology in HVAC water circuits has continued to be an abiding interest .
OZONE IN AIR
By Charles Nicolson
Like oxygen , ozone is a gas , small amounts of which are formed in the atmosphere by incoming solar UV radiations .
Courtesy Ozone Service Industries .
Ozone is heavier than oxygen so ozone in the atmosphere tends to sink , but seldom descends very far because O 3 molecules are so highly reactive that they either combine with each other [ 2 x O 3 forming 3 x O 2
] or react with other gaseous or particulate substances in the atmosphere .
This highly reactive character of ozone is what makes ozone useful not only as a powerful quick-acting disinfectant which chemically destroys micro-organisms , but also as an extremely efficient deodorising agent which acts by oxidising the organic debris from the dead micro-organisms as well as any other odourproducing organic and inorganic contaminants .
Furthermore , ozone has the capability of bonding particulate airborne matter into larger particles enabling more efficient scrubbing and removal of them from airstreams . The result is sanitised and deodorised air .
Like other powerful non-visible gases , ammonia for example , low concentrations of ozone in air are detectable by odour which can be useful as a natural safety warning . Unlike the sharp harsh odour of ammonia however , low levels of ozone have the clean slightly sweet , pleasant aroma associated with unpolluted country air due to atmospheric ozone formed by solar UV which continuously reacts with and de-odorises all the less pleasant emissions from plant and animal life ( and death ).
The fact that ozone has become so widely used worldwide is due to its efficiency at small concentrations . Also , the limits used
Figure 1 : Human tolerance levels to ozone . are much higher than the concentrations at which ozone can typically be smelled . Generally , an individual can detect ozone at concentrations ranging from 0.01 to 0.05 ppm by volume . However , repeated exposure to ozone tends to raise peoples ’ odour detection thresholds , therefore ozone monitors should be installed in workstations where continuous or repeated ozone exposure occurs .
In Figure 1 , both the horizontal TIME MINUTES and the vertical PPM axes are logarithmic to accommodate both very low ozone ppm levels for up to almost a week of time and extremely high ozone ppm levels for less than 10 seconds .
The lowest symptomatic level shown by the red curve is ozone at 0.1 ppm , which is the maximum weighted average generally recommended . Using ozone in air at ppm-time quantities in the area below the red symptomatic curve will not , therefore , create a health hazard .
However , to avoid any inadvertent ozone concentration increases , automatic or manually operated ozone sensors can be installed to modulate or shut down ozone generators if required . These sensor / shut-down units are particularly important for static air volumes where there is little or no ventilation which are treated by ozone to prevent microbiological degradation in , for example storage places of historical artefacts and documents .
In general , the safety history of ozone usage in air has been very good , helped by the fact that ozone in air is continually reverting into normal oxygen . So far as is known , there have been no formal complaints concerning ozone safety lodged since the original environmental protection agency guidelines were issued in 1986 .
In theory , fast acting ozone leaving no residue seems to be a very promising candidate for periodic cleaning and sanitising ductwork during intervals when areas receiving conditioned air are vacant . However , repeated doses of ozone produce accumulated corrosion on galvanised steel or any stainless steel
48
RACA Journal I September 2021 www . hvacronline . co . za