MIL-HDBK-1191
- Growth support deposits or coatings in system piping or
equipment (e.g. scale, sediment, biofilm).
- A water temperature range of 25-42 degrees C (77-108
degrees F) of both supply domestic cold and hot water systems, including
temperature at fixture discharge, hot water generator, hot water return
distribution systems, and in storage or holding tanks,
- Stagnation in tanks, and supply and return distribution
systems, for both cold and hot water.
Legionella bacteria become aerosolized in moisture droplets of less than
5 micrometer diameter (optimum transmission droplet size for sustained
suspension in air), created by shower heads, faucet aerators, spray
nozzles, respiratory equipment, water impacting on hard surfaces, and
bubbles breaking (such as occurs in hydrotherapy bath whirlpools).
Practical means for altering the aerosols that can lead to legionella
infections are limited.
General Design Considerations. Legionella protection guidance
9.1.6.2
is provided in applicable locations throughout this Section; however
designers should also carefully consider provisions in the latest
editions of the guidelines referenced at 9.1.5 above. Healthcare
facility operational procedures for legionella control, such as cleaning
or decontaminating of respiratory equipment and environmental sampling,
are addressed in the referenced guidelines. The referenced guidelines
also address disinfection techniques for reducing Legionella colonization
in existing facilities, such as superheated water flushing and
hyperchlorination shocking. Generally speaking, the goal of the
legionella-protection design is not to eradicate the bacteria, but to
prevent or limit colonization.
9.2
Potable Water Supply System,
Quality. All potable water supplies shall have an
9.2.1
established potability monitoring program to be acceptable for use by an
MTF. When an MTF project includes a non-potable water service (i.e.,
"gray water") for systems such as irrigation, heating, or cooling, the
design shall provide for requirements for signage, pipe labeling, and
other means as needed to clearly identify the system (including outlets)
as unsafe for human consumption.
Continuity of Service. To the extent economically
9.2.2
practicable, provide a minimum of two water services for hospitals, with
each service fed from separate mains and sources, and designed for full
demand (serving potable, process, and fire protection systems).
These
services should enter the building at separate locations. The purpose of
this provision is to provide an uninterrupted supply of potable water, or
permit swift service restoration, in the event of a water main break. If
two separate water sources are not practically available, on-site storage
shall be considered. Where practical, loop the mains around the facility
and provide sectionalizing valves.
Backflow Prevention, General. The flow of non-potable water,
9.2.3
or any other nonpotable liquids, into the potable water supply shall be
prevented. Necessary measures to prevent backflow, cross connection, or
9-3
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