Chemistry and Chemical Disasters. A flammable liquid gives off a vapour which can be readily ignited at normal working temperatures. Under the Canadian Controlled Products Regulations, a flammable liquid is a liquid with a flash point (using a closed cup test) below 37.8 degrees C (100 degrees F). The US Hazard Communication Standard uses a similar, but not identical, definition. Flammable liquids can be extremely hazardous in the workplace; for example: If there is inadequate ventilation, vapours can travel considerable distances to a source of ignition and flash back to the flammable liquid. It may be difficult to extinguish a burning flammable liquid with water because water may not be able to cool the liquid below its flash point