In a collaborative research project with CAFS Unit Inc., researchers at the Institute for Research in Construction's (IRC) Fire Risk Management Program have shown that water-mist fire- suppression technology works well in extinguishing fires in large industrial oil cookers. These cookers are used in food processing plants to deep-fry chicken, fish, potato products, dough-nuts and other foods.
When fires occur in these cookers, they are challenging to extin-guish. With oil varying in quantity from hundreds to tens of thousands of litres, the fire can spread rapidly over the oil surface to form a large fire. The oil becomes very hot (up to 407 degrees C) after ignition, and if the oil is not cooled suffi-ciently as the fire is being extin-guished, the fire can re-ignite.
Until now, carbon dioxide has been the most commonly used fire-control agent for industrial oil cookers. Although it works well in extinguishing flames over the oil surface, it does not have sufficient cooling capacity to bring the oil below its auto-ignition temperature and prevent it from re-igniting. Chemical extinguishing agents are not an alternative because they are not allowed in food processing plants.
IRC researchers have come up with a viable option: they have found that fine-droplet water mist (large water droplets splash the oil from the cooker) does a good job in extinguishing commercial cooking oil fires and preventing re-ignition. This work builds on IRC research on water-mist fire suppression tech-nology over the last decade.
Based on this experience, the researchers have taken on this challenge and developed two water-mist systems for extinguishing these large cooking oil fires. Using a simulated industrial oil cooker 2.44 m wide and 3 m long, and holding up to 1,000 litres of canola oil, they stud-ied both the characteris-tics of water mist and the required design parame-ters for the use of water mist in extinguishing such fires.
Both of the water-mist systems they had devel-oped were effective in extinguishing the cooking oil fires with short extin-guishing times. The fine water droplets penetrated the fire plume and reached the oil surface. Oil temperature quickly decreased with water-mist discharge. No burning oil was splashed outside the cooker, and no cooking oil re-ignited in the pan. The effectiveness of water mist in fight-ing large cooking oil fires was influ-enced by the spray pattern and coverage, water density distribution, and water spray momentum. With the success of these fire tests, water--mist systems based upon this research will soon become available to the industry.
Specific questions on this project can be directed to Dr. Zhigang Liu at (613) 990-5075, fax (613) 954-0483, or e-mail zhigang.li u@nrc-cnrc.gc.ca. This article originally appeared in the Sept. 2003 issue of Construction Innovation, a newsletter published by the IRC.
