Ensuring safe operating conditions

Understanding the effect air can have on operating conditions can be the difference between being a leading institution, or a liability, to the industry. In high risk environments there are methods imperative in maintaining sterile conditions.

The best place to start is outside of the sterile environments, where ‘dirty’ becomes ‘clean’. While there are standards and guidelines to meet inside the clean rooms, achieving and maintaining these goals begins with the air handler.


HEPA filters are the providers of clean air when installed and maintained correctly. However, the filtration that protects the more expensive HEPA filters is in the air handler. Many products serve this purpose, some are poorly designed and can cause the HEPA to have a shorter life. Floppy pocket installations can cause particles to shake loose into the system when pressure drops occur. This results in the HEPA filters processing heavy dirt instead of its intentional filtration of ultra fine particles. This in-turn shortens the lifespan of the only filtration providing clean air.

HVAC hygiene

HVAC hygiene is often trusted to the mechanical services contractor and forgotten about (in faith) until there is an issue. Having an educated service provider on HVAC hygiene can improve the sterile environments condition over its lifetime.

Mould grows and flourishes in dark damp environments and can be carried by the velocity of air to the HEPA filter. The HEPA is a celluloses material very susceptible to becoming a food source for mould. Mould presence will compromise the function of the HEPA filter and therefore become part of the contamination within the‘sterile’ environment.

Duct and HEPA integrity

Having a HEPA filter at the end of a HVAC system doesn’t mean the environment it serves is ‘sterile and clean’. If there is leakage in the duct work not only is there an energy consequence but there may be additional issues. If the duct leaks into the roof space and pressurises the ceiling it can then become an unintended dirty air supply, spilling into the operating theatre. This may happen via light fittings or other penetrations for services in the ceiling space—even around the HEPA filter housing box. Air leakages can be an almost hidden way for poor quality air intrusion into the clean zone.

Air change rate and room pressure

These can go hand in hand—increase in the air change rate allows an increase in room pressure. There are three zones of air in an operating theatre environment that we must maintain.

  1. The operating zone— the cleanest area or laminar air flow from the HEPA filtration above, this creates a zone of sterile air directly down protecting the operating zone of external air movements which are more dirty.
  2. The inner zone—this is the room space itself. Although served by HEPA filtration the air here has likely already hit the ground and other surfaces and is then considered unclean and may stir up fibres and other particles in the room. This zone must be higher pressure than the external zone.
  3. The external zone— the adjoining rooms and corridors to the inner zones room are the external zone. These areas are less clean than the inner zone and as this is the case must be a lower pressure in order to protect the sterile operating area.

By maintaining the air quality appropriately in these clean rooms, not only do we provide the best possible, safe environment, but we also save energy and minimise costly repercussions.