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Warm Water Nurtures Airborne Hazard
December 22, 2011
Mixed Regulatory Signals Complicate Legionella Control
By Barbara Carss
Regulators are increasingly targeting cooling towers in an effort to arrest the source and propagation of legionella bacteria responsible for serious and sometimes fatal lung infections. At the same time, they face some conflicting pressure to revise longstanding controls on a more common host to legionella – a building’s potable water system.
Legionella moves throughout a building when it is aerosolized. That is, carried in very fine water droplets that humans can inhale. Thus, cooling towers, shower/bath fixtures, saunas, hot tubs and decorative fountains are particularly suited to transmit the bacteria, but it can also flourish and spread in other piping networks, even cold water supply when it warms to temperatures greater than 20°C (68°F).
Building managers/operators should particularly watch for so-called dead legs, which are sections of pipe where water sits unmoving for days at a time. A water pressure differential can draw that stagnant water into the potable supply, carrying contamination with it.
“Risk management should really be done proactively with respect to water systems,” advises Bernard Siedlecki, Senior Associate, Indoor Air Quality & Microbial Contamination, with the consulting firm, Pinchin Environmental Ltd.
“Time and time again, we get involved when people are in reactive mode. They should be aware that in the event of an outbreak, or even one infection, they will be subject to scrutiny from Public Health and possibly from the Ministry of Labour.”
The Canadian Commission on Building and Fire Codes has just released proposed changes to the National Building Code that would: impose minimum distances between cooling towers and a building’s air intake and exhaust vents; mandate backflow prevention devices and other drainage controls; reference ASHRAE guidelines for reducing legionella risks; and require access ports, service platforms and fixed ladders to provide ready access for inspection, monitoring and testing of cooling towers.
The proposals, which will be open for public comment until December 16, 2011, respond to outbreaks of legionellosis in recent years that were traced to mist dispersed from cooling towers. Designers, developers, building owners/managers and local building officials have expressed a need for formal guidance in identifying and mitigating risks.
“That’s how changes come about. Somebody says: we need to do something about this,” reflects Diane Green, Technical Advisor for HVAC and Plumbing with the Canadian Codes Centre at the National Research Council. “If these changes are approved and adopted by the Provinces and Territories then there will be regulations.”
Building owners/managers in the City of Hamilton must already comply with North America’s first municipal by-law aimed at cooling towers, which requires owners to register their cooling towers and develop risk management plans. The by-law references an Australian standard along with guidance documents from ASHRAE and the Cooling Technology Institute.
TEMPERATURE TEMPEST
Meanwhile, domestic hot water presents a health and safety conundrum. Risk mitigation can create a competing risk, and safety advocates with differing priorities continue to debate the appropriate water temperature to best safeguard building occupants.
Proponents of lower hot water temperatures to prevent scalding appear to have won the argument in Ontario, where two key regulations dictate a maximum temperature of 49°C (120°F) for water distribution. Critics counter that the Ontario Building Code (OBC) and the Long-Term Care Homes Act now enshrine conditions that enable legionella to thrive.
“That really puts us in a bind,” observes JJ Knott, President of the Canadian Healthcare Engineering Society (CHES) and Director of Maintenance at the Norfolk General Hospital and its associated long-term care facilities in southwestern Ontario. “Legionella grows in temperature ranges up to 50°C.”
New construction complying with the OBC typically incorporates mixing valves so that hot water can be stored at a temperature lethal to legionella – conventionally, 60°C (140°F) – then diluted with colder water as it moves from the storage tank to outward delivery points. In contrast, many of the older facilities captured under Ontario’s 2010 long-term care homes regulation do not have this plumbing flexibility so building operators are forced to lower storage tank temperatures in order to meet the requirement.
Contradictory advice abounds. Notably, the proposed new ASHRAE Standard 188, Prevention of Legionellosis Associated with Building Water Systems, recommends that hot water be stored at temperatures no less than 60°C and circulated at a minimum of 51°C (124°F) in health care facilities, nursing homes and other building facilities classified as high-risk. The Building Owners and Managers Association (BOMA) of Canada’s BOMA BESt environmental performance benchmarking program currently recommends a hot water distribution temperature between 50° and 55°C (122° to 131°F).
In 2007, developers of Canada’s National Plumbing Code withdrew a proposal for a 49°C maximum circulating temperature following largely negative response in the associated public consultation. Even so, the NPC proposal stipulated a hot water storage temperature of 60°C.
Knowledgeable insiders worry that some building managers/operators are either uninformed or too lackadaisical about the appropriate temperature setting for storage tanks, particularly when they are looking for ways to reduce energy costs.
“Turning down hot water temperatures, especially at night, or installing timers on circulating pumps is widely accepted,” reports Brad Arnold, President of the plumbing services firm, Bradley Mechanical. “I have always vigorously fought this suggestion from managers, superintendents or energy providers. There has to be an education program or process to make plumbers, apprentice plumbers, contractors and building maintenance staff aware of the hazards.”
COMPETING INTERESTS NECESSITATE VIGILANCE
JJ Knott relies on vigilance and preventative measures to deal with the dilemma of Ontario’s rules.
“We test our systems, as do most health care facilities, on a regular basis. That includes our cooling tower and our domestic hot water system,” he says. “We are careful not to use aerators. Those are places where legionella can make a nice home for itself.”
There are also chemical-based options for destroying the bacteria. Indeed, this is the approach that various standards and guidelines recommend in vulnerable areas where proactive precautions are required and/or to remediate contaminated systems.
This must be done cautiously, however, since biocides can also be aerosolized and harmful to human and environmental health. “It’s not the preferred option to treat water systems with chemicals,” Knott asserts.
Commercial building operators might assume there are fewer risks in their washrooms, which typically do not feature showers or bathtubs where water is more likely to be aerosolized. However, electronic hands-free faucets, which are increasingly being adopted as a water-conserving measure, could introduce a new risk factor. Water supply to the basins is typically lukewarm, while the fixtures’ more complex inner workings can hold water for sustained periods.
In the United States, administrators at John Hopkins University Hospital were recently prompted to remove electronic-eye faucets and replace them with manual models after researchers found a higher level of bacteria, including legionella, within the hands-free fixtures. An associated report from John Hopkins recommends that manufacturers pursue design improvements so that more facilities could assuredly capitalize on water-saving technology.
Ontario’s new Water Opportunities and Water Conservation Act includes an amendment to the Building Code Act requiring a review of water conservation standards at five-year intervals. This could be a way to ensure that water-saving technology is recognized as it becomes available, but it brings new potentially contradictory objectives to a crowded field of considerations for code developers. National code developers are also contemplating broadening the scope.
“Two of the National Plumbing Code’s objectives are health and safety. It does not, at this time, have an objective for water efficiency,” Diane Green says. “But we are very much aware that there can be competing interests.”
National code developers are also watching for the official release of the ASHRAE 188 standard, which is expected later this year or in 2012. Standards that set out best practices tend to be referenced in the appendices of construction codes as additional information, or in relation to specialized occupancies where a level of performance above the minimum building code standard is mandated, but Green reiterates that nothing will be decided until the standard is actually finalized and available.
Even so, Siedlecki notes that there is the potential for any acknowledged best practices standard to come into play in the event of an outbreak and follow-up litigation. Investigators and/or lawyers for a plaintiff could argue that building owners/managers should have reasonably been aware of the standard.
“The document [standard] by itself is not a regulation, but it could be referenced by the Ministry of Labour, for example,” he explains. “The Ministry of Labour does have a bulletin reminding employers of their obligations under the Occupational Health and Safety Act and it does specifically talk about legionella.”
For more information about proposed changes to the National Building Code, see the web site at www.nationalcodes.ca/eng/public_review/2011/introduction.shtml. For more information about the proposed ASHRAE 188 standard, see the web site at www.ashrae.org.
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