Appendix M - Engineering Technical Advisory_Legionellos Mitigation Actions.docx

Appendix M – Engineering Technical Advisory: Legionellosis Mitigation Actions Engineering Technical Advisory Legionellosis Mitigation Actions

In light of the recent Legionellosis outbreak in NYC that was linked to water cooling towers, we highly recommend your Operations Flight conduct a field review of cooling tower and accomplish the actions listed below.

BACKGROUND:

Legionella is a common parasitic bacteria that is found in most U.S. lakes & steams. Some legionellae survive water treatment and are introduced into the public potable water system which only becomes an issue when the bacteria are in high concentrations. This is the usual pathway into water cooling towers (ref: ASHRAE Position Document on Legionellosis, 25 Jun 1998). Legionellae reproduce rapidly in the presence of other simple-celled organisms (such as protozoa and amoebas) who are their parasitic host.

The protozoa & amoeba populations are supported by the usually green biofilm or algal slime food source that frequently grows in poorly maintained water cooling towers. Legionella concentrations are therefore amplified due to poor water cooling tower maintenance. Legionellosis (infection from the Legionella bacteria) results when the bacteria is inhaled or aspirated into the lungs. There is no record of infection due to contact with someone with Legionellosis (see https://www.ashrae.org/FileLibrary/docLib/Public/20091215_ashraed2830320060711.pdf). Water cooling towers are known breeding grounds for Legionella.

ACTIONS.

1.) Identify all operational water cooling towers and inspect them for biofilm growth. Please insure that AF Form 1457s are being maintained and processed on cooling towers identified (per AFI 32-1054, CORROSION CONTROL).

2.) Where water towers are found fouled with biofilm/algae, remove them from service for immediate cleaning and decontamination. Use hyper-chlorination or thermal disinfection (steam cleaning). Be sure to have personnel use appropriate personal protective equipment and coordinate with the Base Bioenvironmental Engineer if you have any questions. As part of the recurring chemical water treatment, we recommend adding a biocide at appropriate intervals to eliminate a known amplifying factor in the Legionella food-chain.

3.) Check the towers to confirm that drift eliminators are installed and functioning properly.

4.) Insure that your water cooling towers are a sufficient distance away from a facility's fresh air intake vents. Currently, this is a subjective assessment (UFC 3-410-01, HVAC, Appendix B recommends a minimum of 30 feet) since there are no required minimum distances prescribed. However, under no circumstances should a facility's intake vent be beside or above a water cooling tower's exhaust plume. If so, take action to provide adequate separation.

5.) Consider replacing your dedicated facility water cooling towers with a dry cooler (especially in out-of-the-way and hard to reach areas where water cooling towers are often forgotten and neglected). While a bit less efficient, these devices remove the open water loop which completely eliminates the Legionella risk. We do not recommend removing water cooling towers from manned chiller plant facilities as these are easier to inspect and also rely on the higher efficiency of the water cooling tower.

6.) Carefully consider implementing ASHRAE Guideline 188-2015, "Legionellosis: Risk Management ..." procedures at their respective base. This may require assembling a cross-functional team from CE, Bio-Environmental, and Base Safety. The document can be procured through your local library for $58 at https://www.ashrae.org/resources--publications/bookstore/ansi-ashrae-standard-188-2015-legionellosis-risk-management-for-building-water-systems.