Emergency Safety Showers Pose Serious Legionella Risk on Mine Sites in remote hot environments
In our last post, we covered the potential hazards of excess water temperatures in the safety facilities on mine sites.
We now want to cover another potential hazard when using an eyewash safety shower and this involves the Legionella bacteria.
Legionellosis is contracted when a susceptible person inhales water aerosols which contain the Legionella bacteria. A study by the Lovelace Respiratory Research Institute in the US found that aerosols generated by a shower increase with flow rates and that a shower dispensing 38oC water will generate 50 – 100 times more aerosols than a shower dispensing water at 25oC.
Any water source with the potential to create water aerosols has the potential to transmit the disease when the water is contaminated with Legionella. These sources include emergency deluge systems, above and below ground storage tanks which feed aerosol generating equipment; and any water system that generates an aerosol and the water temperature ranges between 20 °C and 45 °C.
The proliferation of Legionella bacteria is known to be promoted by:
- a wet, warm environment (temperature range of 20 °C – 45 °C)
- stagnation or low water turnover
- high microbial concentration, including algae, amoebae, slime and other bacteria;
- presence of biofilm, scale, sediment, sludge, corrosion products or other organic matter;
- degraded plumbing materials, such as rubber fittings, which may provide nutrients to enhance bacterial growth and shower head aerators and screens which can limit flow and harbour the bacteria.
The study also found that a person showering under a 9L/min shower for ten minutes will inhale 11 – 14 mg of water aerosols. Showering for a minimum of 20 minutes under a deluge shower dispensing 75 L/min will expose a susceptible person to a significantly high risk if the source water is contaminated with Legionella bacteria.
The Code of Practice for Prevention and Control of Legionnaires Disease recommends immediate online decontamination if a potable water distribution system becomes contaminated with legionella bacteria and test results are above 10 CFU/ml per Australian Standard AS/NZS 3666.3
Cooling Tower source water containing contamination levels 10 – 99 CFU/ml is classified as a moderately high level of concern which is approaching levels that may cause an outbreak and a contamination level >99 CFU/ml is classified as a high level of concern and which has the potential for causing an outbreak.
Inhalation of aerosols while standing under a 100L/min deluge shower for twenty minutes poses a far greater threat at much lower contamination levels.