Feb 2017: Legionella and the role of drift eliminatorsFebruary 15th, 2017
Download PDF: ‘Legionella and the role of Drift Eliminators‘
Drift eliminators are the most critical component in a cooling tower relating to health and safety. They are the last line of defence against Legionella.
Legionella bacteria in cooling towers is controlled by two critical elements:
1. The water treatment program – the first line of control.
2. The function, design and condition of drift eliminators – the second line of control.
But what if the water treatment program fails for a few days?
This could be due to:
- Power loss to the chemical dosing equipment (tripped fuse)
- Empty chemical drums
- A broken plumbing line from the dosing equipment to the cooling tower
If the water treatment program fails in any way, drift eliminators are the back-up control measure. They are the last line of defence against Legionella bacteria.
Drift eliminators are extremely important in the attempt to prevent Legionnaires’ disease. This is because they restrict water droplets from leaving the cooling tower via the force of the fan. The droplets, known as ‘drift’, have the potential to harbour bacteria and pathogens such as Legionella.
These droplets can be inhaled by persons within a 2 km radius.
The drift eliminators are designed to control these droplets from becoming airborne and transmissible to people in the area, thus reducing the risk.
Excessive drift loss occurs in the following instances:
- If drift eliminators are not fitted correctly; or
- If drift eliminators are damaged, scaled, dirty, corroded or brittle.
It is highly recommended that they be replaced if defective; that they be removed and cleaned regularly; and inspected to ensure they are fitted correctly.
Cooling tower drift loss rates
(Assumes air conditioning cooling tower 2.4m x 2.4m running for an 8 hour day; 34.7 litres/second recirculation rate; 1,000,000 litres circulated)
- Drift loss based on Coolclean drift eliminators (0.001%): 10 litres/day
- Drift loss based on AS 3666 drift eliminators (0.002%): 20 litres/day
- Drift loss estimated if dirty, scaled, corroded or brittle (0.005%): 50 litres/day
- Drift loss if damaged or incorrectly fitted (conservative estimate 0.02%): 200 litres/day
Every single drop of drift has the potential to contain many legionella bacteria. Drift reduction is a major benefit and safeguard. If less than 10 CFU/ml (legionella) is classified as safe, what is the potential impact of 10lt, 20lt, 50lt or 200lt of drift loss in 8 hrs? What if the count is over 10 CFU/ml?
There is a need for more focus in maintaining cooling towers based on performance and legionella control. The water treatment is currently the main focus when it comes to cooling tower maintenance. How the cooling towers perform mechanically tends to be overlooked.
We come across many cooling towers in Melbourne with drift eliminators that are not inspected and maintained correctly.
DRIFT LOSS IS WATER LOSS
How often are your drift eliminators being checked and maintained?
Best practice is 3 monthly, in line with cooling tower manufacturers’ specifications, as generally stated in their operation and maintenance manuals.
The routine cooling tower clean is a great time to remove, inspect and clean the drift eliminators. We also recommend that photos are taken at this stage to prove that they are in good order. This is part of Coolclean’s standard routine clean procedure.
As a cooling tower specialist company, our focus is on all cooling tower components, but especially on the last line of defence against Legionella, the drift eliminators. No drift loss equates to no Legionella bacteria issue; very low drift loss equates to very low chance of Legionella.
Coolclean provides cleaning, repair and replacement of drift eliminators. We supply quality PVC drift eliminators, which are rated at a maximum drift loss of 0.001% of the recirculated water rate. This is well within Australian Standard requirements of 0.002%.
In summary, well maintained drift eliminators stop drift loss and control risk:
- Preventing the spread of Legionella bacteria
- Improving system efficiency
- Saving on water and reducing loss of treatment chemicals
- Avoiding damage to nearby roofs, buildings and cars – from chemicals contained in excessive drift
Contact us for assistance or advice.
Coolclean is based in Melbourne. We service Victoria, NSW, SA and Tas.
Unit 21, 21-22 National Drive, Hallam VIC 3803
+61 03 8765 9500
Level 7, 91 Phillip Street, Parramatta NSW 2150
+61 02 8893 1241
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