Bio Hazard Risks and Tips to Avoid Them

Summer is here, which means our HVAC systems will be working hard to keep us cool and comfortable. While your HVAC system can help you and your employees beat the heat, did you know that systems running in damp/humid conditions pose significant health risks? Well, they do, including mold, bacteria and legionella (which causes Legionnaires’ disease). Before reopening a building, be sure to take steps to protect employees and visitors from potentially harmful microbes. 

Health Risks Associated with Microbial Growth

Mold, legionella, and other microbes can grow in areas with excess moisture and stagnant water. These agents can cause a range of illnesses, from mild allergic reactions to acute respiratory illness.


Legionella grows primarily in stagnant or standing water found in unused plumbing and other inadequately maintained building water systems.  
Inhaling legionella can cause Legionnaires’ disease. Legionnaires’ disease is a severe form of pneumonia with symptoms including cough, shortness of breath, fever, muscle aches and headache. According to the CDC, Legionnaires’ disease has a case-fatality rate of about 10%.


Moisture intrusion from the exterior building envelope, internal moisture sources, and elevated relative humidity can all give rise to mold growth within buildings on materials such as carpet, wallboard and other furnishings.  

Elevated indoor mold concentrations most commonly results in allergic reactions, such as sneezing, coughing, and itchy eyes. People with asthma or compromised immune systems may develop more severe illnesses, including respiratory infections and sinusitis. Some molds also produce mycotoxins, which are associated with a range of adverse health effects when found in high concentrations.  

Tips for Reducing Legionella Risk

You can lower the risks of legionella by implementing a water management program following ASHRAE Standard 188, minimizing stagnation of water systems during periods of low occupancy, and performing regular maintenance on the following three areas:

  1. Water systems: Flush hot and cold water systems through all points of use, including sinks, showers, and toilets. Allow hot water systems to reach their maximum temperature (but avoid scalding risks). Minimize splashing and aerosol generation during flushing. Systems that have been stagnant for extended periods may require more advanced disinfection measures.  
  2. Cooling towers: HVAC systems that use cooling towers can have legionella that proliferates when not properly treated or operated at a reduced capacity. Before reopening facilities, be sure to deep clean cooling towers following manufacturers’ guidelines, removing visible slime, debris, and biofilm.
  3. Water-using equipment: Drain, clean, and disinfect fountains, ice makers, pools, spas, and other water-using equipment that have been idle. Also, flush and treat safety equipment such as fire sprinkler systems and eyewash stations before reopening buildings.

Tips to Reduce Mold Health Risks

Free Course

The Construction Safety Council offers a virtual Infectious Disease Course on Wednesday, June 29. This course will show participants how to sample air for mold and moisture and remediate areas that harbor mold. By the end of this course, participants will be able to: 

The best part? It’s free! You can register for the course here.


Protecting your employees from dangerous bio hazards is a must for any property owner or manager. Reach out to the RCM&D risk consulting team with any questions and to learn more about mold and legionella.