Biological Contaminants

Researchers have found air handling systems containing high levels of micro-organisms such as Aspergillus, Penecillium, Alternaria and Cladosporidium all of which are capable of causing allergies, respiritory infections and some cases serious illness.

The term "Building Related Illness" (BRI) describes illnesses caused by microbial contaminants in a building.

Micro-organisms are minute particles of living matter generally known as Viruses, Bacteria and Fungi (yeasts and moulds).

Often found growing in the most inhospitable conditions, they are extremely adaptable.

Dirt accumulation in the air handling systems is inevitable and even in new buildings it is generally "built" into the systems. With time, micro-organisms breed and contaminate all the system.

Micro-organisms taken in through the fresh air intake can also contaminate the system.

A known result can be outbreaks of Legionnaires disease primarily a concern for water cooling towers.

While most micro-organisms will clump together and attach to dust particles many times larger than themselves, they will be retained in the filter, and many more will pass through the filter.

Filters also become reservoirs of micro-organisms and it has also been proven the case even with HEPA (High Efficiency Particulate Air). Even filters commonly used in hospital air-conditioning systems, allow fungi to grow within a short space of time and produce spores which are then blown via the air stream into the air-conditioned rooms.

Apart from outdoor sources, there are also sources of contamination from within the building.

Occupants release microbes into the air and the return air draws back microbial contamination to the air-handling unit.

If the system is a well-designed one, this air will be mixed with fresh air and efficiently filtered, thus reducing some microbial load.

If system is not well designed, then micro-organisms will pass through filters and may come to rest in the cooling coils or condense drip trays, or in the dirt and dust of the duct work.

From there, they breed and are carried in the supply air to be breathed by the building occupants.