By Danny Cardeso
I recently responded to a tar kettle fire that reminded me of how dangerous such fires can be. What started out as a simple tar kettle fire ended as a second-alarm structural assignment with one single-family house totally gutted, several backyard tool sheds destroyed, a rental box truck obliterated, and a fire company that barely escaped serious injury from a BLEVE (boiling-liquid/expanding-vapor explosion). These incidents must be approached with caution, and, barring any immediate life hazard, a defensive mode of operation is in order.
PROPERTIES OF ROOFING TAR
Roofing tar is produced in large, solid, 100-pound cylindrical pieces called “kegs” or “sticks.” Tar is actually a misnomer, because the product used in roofing is actually a form of asphalt. Asphalt is often mistakenly confused with tar because the appearance is similar and the substances may be used interchangeably in many industrial processes. Asphalt, known in Europe as “bitumen,” is a dark brown or black substance derived from crude oil. Tar, on the other hand, is derived from coal products, which are chemically and physically different from asphalt.
 (2) Following a BLEVE, the fire progresses to two alarms, and this house is destroyed. (Photo by Ricardo Rodriguez.) |
There are two main types of asphalt: straight run asphalt, or asphalt cement, and air-blown or oxidized asphalt. The latter is used in roofing and has a high softening point. It may be found in a solid, semi-solid, or liquid form, depending on its temperature.
Roofing asphalt is available in four types or grades. They are classified as I to IV, with III and IV being the most commonly used. Depending on the specific type (I to IV) and manufacturer, roofing asphalt has a boiling point of 650°F to 1,000°F, a flash point of ≥450°F, an autoignition temperature of ≥600°F, a flammable vapor range of 0.9% to 7%, and a softening point of 135°F to 225°F. Recommended application, or as it is known in the industry, equiviscous temperatures (EVT), for mopping grade roofing asphalt also varies by type and ranges from 330°F to 444°F. For the purposes of this article, roofing asphalt will be referred to as roofing tar or simply tar.
SCENE SIZE-UP
Because of the relatively close application temperatures (330°F to 444°F) and flash point (≥450°F) of roofing tar, roofers tending a tar kettle must carefully watch the temperature to prevent tar from overheating and igniting from the kettle’s propane burners or autoignition (≥600°F). To compound the problem of temperature control, the vast majority of tar kettles used in the industry are not equipped with temperature sensing/control devices. Once ignited, the result is a stubborn fire that can reflash despite attempts to extinguish it with on-site extinguishers.
Many questions must be answered on arrival prior to deciding on your course of action. Where are the propane cylinders used to fuel the tar-heating burners? On arrival, ask the members of the roofing crew if they have secured and accounted for all the propane cylinders. In the fire mentioned earlier, the roofing crew told the initial arriving company that they had removed the propane cylinder. What they failed to mention was that they had not accounted for their spare cylinders. The resulting BLEVE of a 100-gallon propane container drove home the lesson, “expect multiple cylinders.”
 (8, 9) Unsuccessful in closing the lid, the crew attacks the fire with a broken stream, created by placing a thumb over the end of the garden hose. |
• Where is the kettle located, and what is its structural integrity? The kettle’s location is going to determine the difficulty or ease of your hose stretch and the entire operation. The difference in the resources needed for a tar kettle on the ground floor within reach of a preconnected attack line and one on the roof of a high-rise building is obvious. In addition, if the kettle is in good structural condition, with its lid present and functioning, extinguishment will be easier.
• What is the size and intensity of the fire? Do you have a small incipient fire, or has it had time to build up? The long-er the burn time, the higher the temperature of the tar inside will be. This translates to a tougher, longer job of extinguishment and greater hazard to the firefighters.
• Are there exposures? Remember that except for possibly some warping, the tar pot will survive the fire just fine. You must focus your attention on any exposures and get water on them as soon as possible. Depending on the tar kettle’s location in relation to nearby combustibles, you could have your hands full with multiple exposures requiring several handlines.
• Is there an immediate life hazard? Unless injured workers are in the immediate area, the life hazard should be minimal unless exposed structures have become involved in fire. The other life hazard threat comes from the potential BLEVE of the LP tanks. If BLEVE is imminent, evacuate the surrounding area a minimum of 300 feet.
SUGGESTED TACTICS
If you are a dispatched single company and your size-up indicates you will need help, get an assignment rolling before doing anything else. The entire crew should be wearing full bunker gear and breathing air from their SCBAs. If your LP cylinders have not been secured and are not exposed to severe heat or flame impingement, secure them. If they are critically exposed (venting pressure-relief device), you have a difficult decision to make. With an immediate life hazard or occupied structures nearby, begin aggressively cooling the tanks from an area of relative safety. Keep your distance, and try to position yourself with some shielding between you and the tanks. A house, a parked car, the tar kettle itself, a large tree, and even your apparatus are better than nothing. If there are no lives at risk, pull back farther and let the fire run its course, protecting exposures without endangering personnel.
If the LP tanks have been removed prior to your arrival, your life just got simpler. In this case, begin with exposure protection and attending to any immediate life hazard. Once these matters have been addressed, or if they are not issues, try to close the lid to the tar pot. You can safely accomplish this with the reach of a pike pole-one firefighter closes the lid as another firefighter protects him with a hoseline. After the lid is closed, begin cooling the outside of the tar pot with short bursts of water fog. This will help to control the fire by reducing air and beginning to lower the tar’s temperature below its flash point, thereby removing two legs of the fire tetrahedron (air and heat).
Sometimes the lids are missing or warped, or you simply cannot close them. In this case, if the fire is small and not very intense, try a dry chemical or CO2 extinguisher. Keep in mind that extinguishers usually won’t work: These fires are beyond the incipient stage because the alarm was delayed while the roofing crew attempted to extinguish the fire (evidenced by used extinguishers scattered on the scene). At this stage, the tar has been burning for a while, and its temperature is well above its flashpoint, maybe even beyond that for autoignition. The extinguishers will knock down the flame by interrupting the chemical chain reaction, but the lack of cooling or effective vapor suppression will allow repeated flashbacks and continued burning.
With a nonfunctioning lid, your other option is to use short bursts of water fog into the burning tar kettle from a safe distance. Expect some hissing and popping, but if you keep your bursts short and wait in between applications, you will extinguish the fire without significant spillover. This intermittently applied short-duration fog stream will flash to steam prior to coming in gross contact with the burning tar. This steam conversion will begin to lower the surface temperature and the vapor pressure of the tar. Furthermore, fine drops of water gently falling on the tar’s surface will begin to form an emulsion that adds to the cooling, vapor-suppressing effect. When properly conducted, with or without extinguishers, this is an effective tactic.
 (12, 13) The crew must remain vigilant until further cooling has occurred. If the tar remains above its flashpoint, it could reignite. |
Water improperly applied to burning liquid tar will cause a violent reaction. Because the tar’s temperature is well above the boiling point of water (212°F), and the floating properties of hydrocarbons (specific gravity <1), water migrating below the surface of the tar will quickly convert into steam, expand in volume, and expel flaming liquid tar several feet from the kettle. The reaction is most powerful when a stream of water is plunged below the surface of the tar. Under no circumstances should a fire stream be directed into the burning tar kettle from close range. The resulting steam expansion/explosion will expel hot burning tar back onto the hose team. (I have witnessed this several times. One time, the nozzleman escaped severe burns only because of the protection provided by his full turnout gear and SCBA.)
AFFF foam is also a possibility, although it is not usually necessary and should be considered only after closing the lid and water fog and extinguisher use have failed to control the fire. Depending on the tar kettle’s location, company staffing, the type of foam application equipment used, and if foam is available on the first-arriving engine companies, the logistics involved in a foam operation may preclude this as an option-or at least greatly discourage it in favor of the other methods discussed.
• • •
Tar kettle fires seldom cause much fanfare, but they should not be taken lightly. The potential for catastrophe exists with each one. A BLEVE is a real hazard. When dealing with your next tar kettle fire, think of your unit as a SWAT team making entry into a house. Gather information, go slow, seek cover, and attack from a distance.
Fortunately, the industry is currently moving away from hot mopped roofing asphalt in favor of less hazardous technologies and products. Currently, hot mopping is more commonly used in three states-Florida, Texas, and New York. One day, this roofing procedure may go the way of the dinosaurs and so, too, will the dangerous tar kettles. ■
Special thanks to Captain Bill Gustin, Miami Dade (FL) Fire Rescue, for his assistance in the preparation of this article.
References
AFSCME Health and Safety Asphalt Fact Sheet. Washington, DC; American Federation of Employees, 1989.
Emergency Response Guidebook, U.S. Department of Transportation, 2000.
Fred Gregson, sales manager, ABC Supply Company Inc., Miami, FL, 2005.
Encyclopedia of Occupational Health and Safety, Vols. I, II; Geneva, Switzerland, International Labour Office; 1983, 199.
Johns Manville “Roofing Asphalt MSDS No.3121,” Denver, CO, May 10, 2004.
Owens Corning “PermaMop MSDS No.15-MSD-19659-01-C,” Oct. 24, 2001.
Protection Guide to Hazardous Materials, 12 ed. (Quincy, MA: National Fire Protection Association), 1997, 325-316.
Valero Marketing and Supply Company “Asphalt MSDS No. 208,” San Antonio, TX, July 24, 2001.
Wess, Joann A., Dr. Larry D. Olsen, “Concise International Chemical Assessment Document 59,” Geneva, Switzerland; United Nations Environment Programme, the International Labour Organization, and the World Health Organization; 2004.
■ DANNY CARDESO is a battalion chief with the Miami-Dade (FL) Fire Rescue Department, where he is assigned to the Operations Division North District. He is an instructor in the department’s Officer Development Program and a part-time instructor at the Miami Dade College Fire Academy.
