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Legionella...How Much Is Too Much??


Access Analytical - Thursday, May 23, 2019

There are some questions that inevitably come up when testing both potable and non-potable water samples for Legionella.....It usually starts off with, "I got my test results back and there is Legionella present!"  And is followed up with,  "Is this bad?  How much is too much?  What do I need to do?"  

All of those are very good questions and sometimes the answers are a bit hard to come by.  In order to address these questions one has to look to the currently established OSHA guidelines for help.  Note that I said guidelines, not law, there is a major difference.  The only state that has established laws in place regarding Legionella contamination is the state of New York, every other state currently follows OSHA guidelines or may have established their own limits in a few cases.

According to OSHA the following limits should be used a guide for deciding on further action:

COLONY FORMING UNITS (CFU) OF LEGIONELLA PNEUMOPHILA PER 100 MILLILITERS OF SAMPLE 
                    Action                     
      Cooling Tower Water     
       Domestic Water           
  Humidifier / Vaporizer Water  
 1
10,000 
1,000 
100 
 2
100,000 
10,000 
1,000 

Action 1:  Prompt cleaning and/or biocide treatment of the system.
Action 2:  Immediate cleaning and/or biocide treatment.  Take prompt steps to prevent employee exposure.

*Note that Access Analytical reports results to 1 CFU per 100mls of sample as listed above.  Other labs 
may express results in different units of measurement.