November 28, 2008

Legionella can spread when dead water in lines grows bacteria. Studies about the specific cause of the disease have focused on HVAC systems and their interchanges.

Health & Safety

Precautions needed to prevent bacteria, illness at demolition sites

DON PROCTER

correspondent

MISSISSAUGA, ON

If precautions aren’t taken, a demolition or renovation site can be ripe ground for the growth of Legionella pneumophila, a bacterium that can cause pneumonia.

Legionella can spread in a number of ways — one means is through water lines. Contractors, particularly during work in partially-occupied buildings, should take care to properly drain and isolate potable water lines in work areas away from main distribution lines.

“If you don’t do this, you get dead water in the lines which will grow bacteria that could contain Legionella which may contaminate main distribution lines serving the remainder of building, ” says Bernard Siedlecki, senior manager, Pinchin Environmental Ltd., a consulting firm based in Mississauga.

Legionella pneumophila came by the name Legionnaires’ Disease after 221 people were stricken with it at an American Legion convention in Philadelphia in 1976; 34 of them died.

In the U.S. 10,000-15,000 people contract legionella and 4,000 die from it annually, according to the U.S. Occupational Health & Safety Administration.

Siedlecki says precautionary measures should be written into the specifications of a project, either by an environmental consultant or an HVAC consultant.

There are some experts who think cooling towers are the most common source of legionella. A cooling tower was believed to be the source of an outbreak that killed 23 people at an old age home in Scarborough in 2005.

More often, the main culprit is hot water storage heaters or potable water distribution systems, according to a study in 1998 by Hodgson and Casey. It found hot water tanks were almost twice as likely to be contaminated with Legionella as cooling towers.

If hot water tanks are not flushed regularly, sediment forms at the bottom where the water temperature is coolest, explains Siedlecki. Legionella could develop in the sediment and be released into the water system if there is a “water pressure disturbance”.

While the Hodgson and Casey study, and others, indicate that cooling towers are one of the least likely sources of legionella, they can, nonetheless, be a problem, especially if dust – such as construction dust – infiltrates the cooling tower, says Siedlecki. Proper maintenance and effective water treatment help minimize the potential for bacterial growth.

This summer the Ministry of Labour conducted a safety blitz at demolition and retrofit projects, taking a “zero tolerance” approach to hazards ranging from asbestos to Legionella.

In Siedlecki’s experience, building owners were diligent after the 2005 outbreak in Scarborough and water chemical treatment companies pushed for better chemical controls. But the message of prevention has been “diminishing” as memories of the outbreak fade.

While there are no regulations dealing specifically with the bacteria, ASHRAE’s Guideline 12-2000 – Minimizing the Risk of Legionellosis Associated with Building Water Systems is available online.

The U.S.-based Cooling Technology Institute offers a best practices guide for controlling legionella in cooling towers which also can be downloaded online; in addition, the Ministry of Labour has issued an Information Bulletin stating that employers have a duty under the Occupational Health and Safety Act to protect workers from the hazard of Legionella exposure, says Siedlecki.

He points out that the bacteria spreads through air, not by skin contact.

“The water has to be aerosolized (fine water droplets) and be inhaled by susceptible persons,” says Siedlecki. “People have to be aware of the bacteria, how it could be stimulated in a building and how to manage it.”

To verify the presence of Legionella, water and swab sampling would be necessary.

Currently, there are only a couple of labs in Ontario that test for legionella, but Pinchin Environmental is expanding its laboratory services to include testing by year’s end or early next year.

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