HEALTH AND SANITATION
29
Superheat-and-flush
disinfection against
legionella outbreaks
By
Environmental Protection Agency, document EPA 810-R-16-001
The superheat-and-flush disinfection method involves raising the
water temperature in the hot water heater sufficiently to ensure
hot water is delivered and circulated to all water outlets.
All outlets include faucets and showerheads, and
then flushing with the hot water for a suitable
period. In building water systems that are not
heavily contaminated, a constant hot water heater
temperature of 60°C (and 55 degrees at the outlets)
is often enough to control (but not necessarily
eliminate) legionella. For example, Dennis et al.
(1984) showed that in a laboratory at 54°C, a 90%
(1 log) reduction in L. pneumophila 74/81 serogroup
1 occurred after 27 minutes. At 58°C, the same
reduction took only six minutes.
Where emergency remediation is required, raising the
temperature of hot water tanks to 71–77°C (160–170°F)
and keeping the water temperature at outlets >65°C
(149°F) during flushing are recommended (Sehulster and
Chinn, 2003; ASHRAE, 2000).
The optimal flush time reported varies from 10 to 30
minutes depending on the characteristics of the premise
plumbing system. A 30-minute flush, first adopted by
Best et al. (1983), is recommended as a good practice.
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CHARACTERISATION OF EFFECTIVENESS
AGAINST LEGIONELLA
The superheat-and-flush method can be effective as an
emergency disinfection procedure for building hot water
systems, particularly in hospital outbreak scenarios.
•
Best et al. (1983) first reported the use of
superheat-and-flush to control legionella from a
hospital water supply by raising the temperature
of hot water tanks as high as 77°C (170.6°F) for
72 hours and flushing the water outlets for 30
minutes with hot water. After flushing, the number
of samples testing positive for legionella was
reduced, followed by a decline in the incidence
of legionellosis. The temperature of the hot water
storage tanks was intermittently increased on eight
occasions to 60–77°C (140–170.6°F), resulting
in a decrease in the number of months in which
cases of legionnaires’ disease occurred and the
proportion of nosocomial pneumonias caused by L.
pneumophila and Pittsburgh pneumonia agent (now
designated L. micdadei).
October 2017 Volume 23 I Number 8