Canadian Occupational Safety

July/August 2020

Canadian Occupational Safety (COS) magazine is the premier workplace health and safety publication in Canada. We cover a wide range of topics ranging from office to heavy industry, and from general safety management to specific workplace hazards.

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F E A T U R E 19 FLAMMABLE LIQUIDS: AIR ON FIRE Flammable liquids ignite easily and are used in almost every workplace. Linda Johnson reports on how workers can prevent these liquids from igniting and on what to do if a fire occurs IN July 2017, an Ottawa roofing company was installing a roof on a two-storey house. Three workers were on the home's balcony when adhesive glue, a flammable liquid, caught fire. No fire extinguisher was available, and the workers had no way to escape from the balcony quickly. Two workers caught fire; the third suffered serious burns to the arms, legs and torso. Flammable liquids produce vapours that can ignite or explode. They are used in a vast range of industries, and most workers will handle them at some time. It's essential for managers and workers to know how to use these chemicals safely and reduce the chance of fire in their workplace. Some of the most familiar flammable liquids include gasoline, paint thinners, cleaners, adhesives, paints, waxes and solvents. Their use is widespread in the automotive, oil and gas, food and which was further divided into Classes 1-A, 1-B and 1-C. Combustible liquids were grouped into Classes 2 (flashpoints between 38 C and 60 C) and 3 (flashpoints between 60 C and 93 C). However, in 2015, the Workplace Hazardous Materials Information System (WHMIS) modified its classification system for workplace chemicals to be more aligned with the Globally Harmonized System of Classification and Labelling Chemicals (GHS). According to WHMIS 2015, flammable liquids are those that catch fire at temperatures below or at 93 C. Moreover, they are now classified into four categories. Flammable liquids that have a flashpoint below 23 C fall into categories 1 or 2, depending on their boiling point. Flammable liquids that have a flashpoint at or above 23 C fall into category 3 (flashpoint up to 60 C) or 4 (flashpoint from above 60 C pharmaceutical industries, as well as in laboratories and in manufacturing machine shops. Flammable versus combustible liquids Flammable liquids are distinguished from combustible liquids by their flashpoint, defined as the lowest temperature at which a flammable or combustible liquid gives off enough vapour to form an ignitable mixture with air. The flashpoints of flammable liquids are lower than those of combustible liquids. Both types of liquid are classified according to their flashpoints and boiling points. Until recently, flammable liquids were considered to be those that had a flashpoint up to 37.8 C, while combustible liquids had a flashpoint at or above 37.8 C and below 93.3 C. The liquids were grouped into three classes, with all flammable liquids in Class 1, but below or at 93 C). The lower the number of the category, the more flammable the liquid is, says Anne-Marie Besliu, occupational health and safety specialist at Hamilton, Ont.-based Canadian Centre for Occupational Health and Safety (CCOHS). A mixture of flammable vapours and air ignites when the concentration of the vapours is within limits known as the lower flammability limit or lower explosive limit (LFL/LEL) and the upper flammability limit or upper explosive limit (UFL/UEL). "If the vapour concentration in the air is less than the LFL/LEL, then the mixture is not flammable because it is too 'lean' to burn. If the concentration of flammable vapours is higher than the UFL/UEL, then the mixture will not ignite because it is too 'rich' to burn," she says. It's important to check the safety data sheet (SDS) of each product handled in the workplace to check for the product's upper and lower limits. This sheet provides key information on the chemical, including its hazards, safe use procedures, protective measures, proper personal protective equipment (PPE) and emergency procedures in case of a fire. Fire and explosion hazard For a flammable or combustible liquid to catch fire, three ingredients must be "The OHS is usually specific to certain processes, where the fire code talks about general use, storage and such. I would check the fire code and then the OHS legislation for the specific requirements." Greg Hodgson, occupational hygienist, University of Alberta in Edmonton

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