Most of the concerns for non-industrial indoor environments have been focused upon commercial office facilities. From an overall health standpoint, a sizable number of people spend a majority of their waking hours in these indoor environments. Close contact with large numbers of people, centralized ventilation systems controlling large indoor environmental zones, and an overall high population density in what is essentially an enclosed box have all made the commercial office building the classic "sick building" candidate.

ASHRAE's definition of an acceptable indoor environment is one in which 80% of the occupants are comfortable and do not express complaints about the indoor environmental conditions. By the very nature of an office environment and the normal stresses of work, the numbers would seem to dictate that there will frequently be complaints about the indoor environment, even in the absence of potential microbial pollutant sources from water intrusion and/or high humidity.

Microbial Room Service

As more and more attention is being focused upon microbial causes of "sick buildings," water intrusion, standing water in the hvac equipment, uncontrolled condensation, and vinyl wallpaper "vapor retarders" have been identified as common culprits. However, building materials and conditions contributing to moisture and probable microbial amplification are not restricted to commercial office buildings.

Hotels, for instance, have individual heating-cooling units located along an outside wall inside guest rooms. Whether these are window units or part of the hvac system, maintenance on individual units is often difficult because of equipment configuration and size, which may make access to coils and condensate pans for cleaning almost impossible.

Similarly, administering a maintenance or filter-change program for numerous individual units is tedious, not only through sheer numbers, but by the necessity to schedule the work when the guest area is unoccupied.

Condensation on windows, which may appear to be little more than an aesthetic annoyance, can in reality serve as a sufficient water source to initiate microbial contamination. Moisture that falls from the windows and/or frame frequently wets the adjacent drywall, which will not dry if covered with vinyl wallpaper. Water overflow from inaccessible condensate pans also results in wetting of drywall surfaces immediately below individual units.

In one sense, hotels have an advantage over commercial office buildings in that occupants are usually present only for relatively short periods of time. Occupants are not as likely to attribute symptoms to the indoor environment as they are in office buildings. This is because their stay is frequently completed before the realization that there may be an association of symptoms with the indoor environment.

Home, Sweet Home?

Residential buildings also pose unique IAQ problems. In multitenant facilities such as apartment buildings, leaks from showers or toilet overflows may impact the individual source tenant, but they invariably have the potential to cause water damage in remote tenant areas by the nature of water movement within the structure. Considering the age of many of the buildings in major metropolitan areas, the potential for widespread water damage (and associated microbial contamination) within walls, ceilings, and similar voids (through which the mechanical system passes) increases as the commonly used iron piping deteriorates over time.

Newer residential construction can also be prone to indoor microbial growth. Basement laundry dryers may not be vented to the outside, often resulting in a fairly constant supply of warm, humid air being deposited into the lower levels of the residence. These areas tend to be poorly ventilated, less likely to be vacuumed and cleaned, and are frequently the site of stored clothing, boxes, papers, and other nutrient sources for mold.

Another common construction practice is to vent bathroom exhaust into a ceiling void space. The introduction of warm, moisture-laden air above ceilings, which may then migrate to the space behind walls, is similarly problematic with regards to promoting microbial growth. In this case, it likely will not be as easily recognized due to the location proliferation of mold in an area not easily accessible or routinely examined.

"Sick" buildings are not restricted to commercial office buildings, so we must always be conscious of the conditions (and not just building type) under which building contamination can occur. ES