Environmental Engineering Reference
In-Depth Information
only provides short-term control. However, if temperature is maintained at
140°F (60°C), the “heat and flush” method will be effective for 2 to 3 years.
Hyperchlorination is also widely used to control
in pota-
ble water systems. Its primary advantage is that it provides a residual chlo-
rine concentration throughout the entire potable water system. It is a rela-
tively costly procedure, and operators experience some difficulty in
maintaining a stable chlorine concentration.
Once building (including cruise ship) management begins a program of
disinfecting hot water systems, it must make a long-term commitment to
maintain the effort. The effectiveness of efforts to prevent the growth of
disease-producing populations of
L. pneumophila
requires continuing vigi-
lance and implementation of appropriate eradication techniques.
L. pneumophila
2.
Hypersensitivity pneumonitis and humidifier fever
Outbreaks or sporadic cases of hypersensitivity pneumonitis and humidifier
fever-type illness can be prevented by the implementation of O&M practices.
The most common apparent source of microbial contamination associated
with hypersensitivity pneumonitis is the condensate drip pan associated
with cooling fan coil units in HVAC systems. Routine inspection and main-
tenance can reduce the likelihood that drainage is impaired and significant
microbial growth allowed to occur.
Drain pans should be sloped a minimum of 0.25” (6.25 mm) per 1.2' (30
cm) toward the drainage point, which should be flush with the lowest surface
in the pan. Water should flow to a trapped water system. Microbial slimes
or biofilms in drain pans and other wet surfaces should be physically
removed by periodic cleaning.
Humidifier fever is reported in Europe, where cool mist humidifiers are
used in association with HVAC systems. These outbreaks of humidifier fever
can be eliminated by the cessation of humidification, replacement of cool mist
humidifiers with steam humidification, or regular cleaning of cool mist
humidifiers to maintain low bacteria levels. Cleaning and maintenance of
water reservoirs in humidifier fever episodes has been reported to be effective
in mitigating symptoms and health complaints. This includes removal of
mineral scale and disinfecting with sodium hypochlorite. Water reservoirs
must be kept free of scale and cleaned with biocides when not in use. Use of
scale and rust inhibitors or biocides on a continuous basis is not recommended
because they may be aerosolized and produce an indoor contamination prob-
lem. In industrial operations, exposure to bacterial endotoxins is a major
occupational health problem. Biocidal treatment of metal cutting fluids and
product wash waters is typically used with limited success.
3.
Asthma and allergic rhinitis
As indicated in Chapter 5, both asthma and allergic rhinitis are caused by
exposure to allergens associated with a variety of organisms. Most com-
monly these include dust mites, cockroaches, pet danders, and mold. Control
