Thursday, 19 January 2012

Ozone Exposure in the Bottling Plant and Measurements

The UK Health & Safety Executive has laid down guidelines for operators exposed to ozone during their working day. These are as follows:

Exposure                 Ozone Level
Max 8 hours         0.067 ppm
Max 5 hours         0.1 ppm
Max 15 minutes         0.3 ppm

0.1 ppm is equal to 0.2 mg ozone per cubic metre of air.

Ozone monitors are available which constantly measure the ozone level in the work environment within the bottling plant. The ozone concentration is shown by a multi-coloured graphical display from green (safe) to yellow (caution) to red (danger). No installation is required and operation is simple. The unit works on batteries or mains supply.  Normal range of detection is from 0.02 - 0.14 ppm.

For those not wishing to invest in a meter, cards are available which may be carried by the operator. Each card can register exposure to ozone by a colour change at 5 different zones on the card.

Measuring Ozone in Water

The method used by many bottling plants involves a colour reaction.  Ozone reacts in weakly acidic solution with dipropyl-p-phenylenediamine (DPD) to form a red-violet dye. The ozone concentration is measured semi-quantitatively by visual comparison of the colour of the measurement solution with the zones of a colour card.  The method is not very user friendly and needs carefully adjustment of pH, mixing of two reagents and  visual comparison of colours.  However, simple, low-cost dissolved ozone meters are available. These measure dissolved ozone in 50ml or 180ml samples. The sensor does not contact the water, so there is no special probe installation. The unit is easy to operate and calibration can be checked by standard kits or ozone sources provided by the manufacturer. The unit can be used with rechargeable batteries or mains application. There are two measuring ranges: 0.02 - 0.14 ppm (mg/l) and 0.1 - 0.7 ppm (mg/l). Accuracy is about 20% and response time between 10 seconds and 1 minute.

If you need a quick, semi-quantitative test, then simple dip strips may be used.

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