The United States Department of Labor's Occupational Safety and Health Administration sets specific guidelines on building and maintenance of HVAC Systems (Heating, Ventilating and Air Conditioning). OSHA breaks down specifics into three groups: 1) system design, 2) maintenance and 3) remediation of a contaminated system.
Guidelines for Designing an HVAC System
OSHA's first guideline is to direct designers to minimize the use of water reservoirs, sumps and pans, and to provide a way to drain water sumps when not in use, such as an electric solenoid valve on the sump drain. The idea is to not let dissolved solids form sediments in the sump. Collection pans should be sloped so water can drain, and the pans can dry. OSHA suggests being careful of where the fresh air intakes are on the system you are designing. Make sure they are not drawing a mist from the cooling tower, for instance. Along these lines, consider prevailing wind direction and velocity, particularly the leeward sides of buildings (the downwind side of the building) and the distance from the cooling tower to the fresh air intake. When designing humidifying systems, do not use raw steam from the central heating boiler to humidify air because it contains corrosion inhibitors and anti-scaling chemicals. Also, confirm that atomizing humidifiers contain contaminant-free water.
How to Maintain an HVAC System
An important part of maintaining a safe and OSHA-compliant system is to conduct regular inspections. Again, standing water is the danger and can lead to microbial and fungal growth. Inspect the entire air distribution system for visual evidence of water accumulation. Regularly drain all sumps and permanently drain inactive sumps. Always drain sumps when the building is not occupied. Be vigilant with fresh air intake airways, particularly in the basement or lower levels of the building because they can easily collect organic material, such as dirt and leaves. Inspect indirect evaporative air cooling systems for leaks that may be injecting cooling tower water into the air stream. Check air-to-air heat exchangers for leaks also. Check all free-standing or portable humidifier sumps to make sure water is not collecting there.
How to Remediate a Contaminated System
In the event that the system does become contaminated, OSHA provides guidelines for remediation. First, eliminate all water leaks and remove any standing water. Replace any water damaged insulation. Operate the HVAC system using only outside air for a minimum of eight hours before returning to normal operation. After returning to normal operation, keep outside air supply rates as high as possible for one month.