There seems to be little definitive statistical research on roofers seriously burned by molten asphalt to a state requiring emergency medical attention. According to the National Institute for Occupational Safety and Health (NIOSH), in 1999 there were 3,600 hot-mix asphalt facilities in the United States. Some 300,000 paving work-ers, 50,000 built-up roofing (BUR) hot-asphalt roofers and 2,000 workers in roofing plants are exposed to as-phalt hazards every day. It is estimated that approximately 2 percent to 5 percent of all new admissions to state burn centers are diagnosed with molten asphalt burns. A few studies have suggested as high as 70 percent of those inpatient treatments were suffered while roofing, with a morbidity rate significantly higher than highway asphalt accidents.
While this percentage could not be accurately verified, I suspect by the exposed nature of the work and higher melting temperatures more BUR roofers would be burned by their asphalt product than pavers. However, when I spoke with several BUR firms in the New England area, they reported no serious asphalt burns in the last three years requiring treatment beyond first aid. Regardless of the burn frequency, it is important for all employers whose employees are exposed to molten asphalt to understand the potential risks of this exposure, safe work practices to avoid physical contact and emergency action plans in the event of a serious burn.
About 99 percent of all the asphalt produced in this country is utilized in roofing and highway products. There are three basic grades of roofing asphalt produced in the United States:
- Straight reduced asphalt is used to make saturated organic felt plies for BUR, asphalt/fiberglass shingles and rolled roofing.
- Coating grade asphalt is used to make asphalt shingles, modified bitumen roofing and rolled roofing.
- Mopping grade asphalt is used in BUR roofing and modified bitumen systems and subdivided into four types based on hardness:
- Type I: Flowable at room temperature. Used on slopes up to 2 percent. Melting point is 135 degrees Fahr-enheit to 151°F.
- Type II: Semi-flowable at room temperature. Used on slopes up to 4 percent. Melting point is 158°F to 167°F.
- Type III: Unlikely to flow at room temperature. Used on slopes up to 25 percent. Melting point is 185°F to 205°F.
- Type IV: Will not flow at room temperature. Used on slopes up to 50 percent. Melting temperature is 210°F to 225°F.
Hazards Associated With BURMop-grade roofing asphalt is typically delivered to the kettle site in the form of 100-pound solid cartons or kegs, which are chopped or split into smaller pieces and placed in the kettle. Tow-behind roofing kettles may range from 25- to 1,500-gallon capacities. On some larger jobs, the oxidized, molten asphalt may be delivered to the job via an insulated tanker truck equipped with onboard heaters and pumps. Liquefied petroleum gas (LPG) is the fuel most often used to fire the burners in a kettle or tanker. Convoluted metal heating tubes uni-formly distribute the burner heat to the contained asphalt, while a pump circulates the molten asphalt, maintain-ing temperature and consistency until the valve is opened and the material is pumped up to the roof deck through the hot pipe. This pipe system consists of multiple, insulated pipe sections (5 to 20 feet in length) joined by common pipe unions. While the product usually loses a few calories in transfer, it is delivered to an insulated container on the roof known as the “hot lugger,” which typically has a 30-gallon to 55-gallon storage capacity. This vessel is generally not heated, which allows the product to cool even more, before it is poured off through a spigot into either individual mop buckets handled by the crew or mechanical felt spreaders.
Once melted, pumped, transferred and mopped in place with either cotton or fiberglass mops, the coal tar is covered with a reinforcing fabric or felt pile for tensile strength and then covered with a subsurface aggregate surfacing material (such as pea gravel, slag or marble chips) for durability. Some roofs are finished capped with a final coat of coal-tar pitch spray and a fine aggregate uniformly applied with a spreader.
The refined, air-blown (oxidized) roofing tar is approximately 450°F in the kettle. According to a 2000 NIOSH study, the optimum kettle temperature for mop-grade (Type I, II, III or IV) asphalt, just before pumping to the roof, is 600°F. This astounding kettle temperature accounts for the significant temperature loss during pumping and pipe transfer up to the roof. At a temperature just above 120°F to 140°F, viscous asphalt can only take sec-onds to create a severe third-degree burn requiring surgery and rehabilitation. The equiviscous temperature (or EVT) is the application temperature range which best adheres the felt and tar once in place by the mop crew. The EVT for roof asphalt is between 330°F and 445°F and depends on the ambient air temperatures on the roof. There is a great number of flammability hazards associated with the asphalt kettle operations, especially in older units not equipped with the state-of-the-art safety devices standard in newer models.
The fumes produced by vaporizing aromatic hydrocarbon compounds may be very toxic and rapidly absorbed by inhalation and absorption by tradesmen constantly exposed (see “Asphalt Fumes in BUR Applications,” Roofing Contractor, May, 2004). Concentrated toxic petroleum distillates such as hydrogen sulfide, benzene, toluene, xylene and naphthalene may be released from the heated product. The NIOSH Permissible Exposure Limit (PEL) to which a worker may be exposed to molten asphalt with no form of protection is a concentration of 5 milligrams per cubic meter of air, determined during any 15-minute period. Chronic exposure may result in minor irritations of the conjunctive tissues of the eyes and mucous membranes of the respiratory tract, irritabil-ity, anemia and irregular heart rhythm. Acute exposure symptoms include nausea and vomiting, diarrhea, rest-lessness, excitation, insomnia and even euphoria. Inhalation has caused central nervous system disruption, con-tracted pupils, dizziness, drowsiness, blurred vision, fatigue, headache, loss of reflexes and convulsions.
Total loss of consciousness, respiratory arrest and sudden death may occur as a result of long-term exposure to highly concentrated asphalt vapors. Asphalt particulates left on the skin of animals in laboratory studies have been reported to result in reactions ranging from mild, contact dermatitis to localized carcinomas. A 1976 NIOSH health study indicated a propensity to exhibit bronchitis, emphysema and asthma when exposed to as-phalt fumes and particulates. Studies have shown that in the roofing industry approximately 68 percent of the complaints were the direct result of first-, second- and third-degree burns. Many of the mucous membrane and respiratory injuries were due to the hydrocarbon solvent exposures due to use of the hot-mop products.
The flash point of the molten asphalt is 560°F. A compound’s flash point is the minimum temperature at which a liquid gives off a vapor in sufficient concentration with air to ignite according to a specific laboratory proto-col. According to a Washington State Dept. of Labor/NIOSH Safety and Health Assessment Program, the as-phalt product temperature should always be maintained at least 25°F below the flash point, as there are a num-ber of unprotected ignition sources on many older kettles. Monitoring the asphalt temperature in various loca-tions may prevent “fallback” due to reduction in the in the softening point of the asphalt caused by overheating the product for prolonged periods. Proper temperature monitoring can also prevent dangerous flash fires with the lid open and kettle explosions with the lid closed and improperly vented. With the lid closed, the fumes in the headspace can build up to dangerous concentrations above the lower explosive limit (LEL) for the product. If the concentration is above the upper explosive limit (UEL), then opening the lid may provide the ventilation to lower the percentage of fumes per volume of air to the point of ignition. If ignition occurs exactly midway between the LEL and UEL, then maximum explosive pressure (MEP) is achieved and the explosive effects of the burn can be catastrophic for anyone near the kettle.
The key to safe and professional quality kettle operation is to maintain a site-specific asphalt temperature just slightly above the EVT. According to a 1996 NRCA study of BUR applications published online by NIOSH (http://www.cdc.gov/niosh/docs/2003-112/2003-112p2.html), there are seven common-sense factors affecting how high above the EVT the asphalt temperature should be maintained:
- Ambient air temperatures and wind speed.
- Total hot pipe pumping distance.
- Pump delivery rate (30-60 gpm).
- Amount of noncombustible, high-R insulation on the hotpipe and lugger.
- Transfer time and distance from lugger to mop bucket.
- Rate of asphalt use.
- Efficiency of closed vessels used on roof.
While a combination of trial-and-error and trade experience will determine the proper, site-specific kettle temperatures, it is always advised to be on the “cool” side until kettle/mop operations are safely improved before temperatures are raised slowly.
Types of BurnsMolten asphalt burns fall into a serious medical burn category called chemical-thermal burns. Burns resulting from hot tar are similar to plastics and flammable jellies (such as napalm) in that the exposed victim himself may become highly flammable. Once absorbed by the dermis, the aromatic hydrocarbon distillates may actually continue to burn inside the body. The petroleum hydrocarbons are released, continue to be flammable once in-fused in the tissue and often reignite deeper in the dermis, often leading to third-degree burns.
The majority of BUR burns result from slips and falls during mopping, most often burning hands and arms. Once arm-burned, victims often fall further into place asphalt, “slipping and smearing” into the product. Unfor-tunately this fall often results in more serious face and eye exposures. Promptly get the victim to professional medical attention. Be careful not to break any skin blisters.
Third-degree burns penetrate both the outer and inner layers of the skin (the epidermis and dermis), sometimes affecting the tissue beneath. A dark brown, “dry meat” appearance indicates a full thickness burn revealing muscle tissue below. The edges of the burn are charred and the surrounding area is leathery or pearly grey. These burns are relative to the high product temperatures found at the kettle. It is often reported by survivors that deep third-degree burns are less painful, as the nerves have been destroyed. This often leads to underesti-mating the injury and delaying emergency response. Deep tissue burns are clearly indicated by the parchment-white tissue totally surrounding the burn, caused by fluid infusion and swelling closing off blood circulation. This area does not change color when pressed, indicating dead tissue. Immediately check the ABC’s - airway, breathing and circulation - and, if certified, provide CPR or rescue breathing when necessary. Next look for and remove any jewelry on the victim as the body will immediately begin to swell with fluids and rings and necklaces can be dangerous. A third-degree burn is often surrounded by peripheral first- and second-degree burns. These areas may be treated by the appropriate first aid methods, including cold running water, applica-tion of a burn ointment, and applying a bandage. Third-degree asphalt burns are covered with the adhered prod-uct and do not require covering with a sterile dressing or clean cloth, as the dressing may become adhered to the tar.
Fourth-degree burns are burns that have gone well into and possible through the muscles and expose the internal organs and bones. Fourth-degree burns are often fatal as vital circulation and central nervous system function cannot be readily re-established.
Once the burned tissue is eroded, the toxic chemicals released from the asphalt compounds can easily enter the circulatory system and lead to systemic poisoning. Immediate water cooling and continuous irrigation not only serves to cool the asphalt and tissue but also dilute and wash contaminates away from open wounds. Severe third- and fourth-degree burns can also destroy larger blood vessels, inhibiting blood supply to critical organs, causing necrosis due to hypoxia (lack of oxygen).
Burns to the EyesAsphalt splash burns to the eyes are particularly destructive, as delicate cornea tissue is easily destroyed. As-phalt workers should be prohibited from wearing synthetic contact lenses (even under safety glasses), as these can quickly melt into the cornea with the intense heat. If the eye burns are internal, continuous, flushing irriga-tion with clean, potable water (or Ringer’s solution) to the open eye is the best emergency treatment. A portable eyewash station is always recommended for every roofing crew. As with all external burns, you cannot over-irrigate or over-cool the burn site. Keep a large, rectangular cooler full of ice water nearby all molten asphalt work for total immersion in just such emergencies. All second- and third-degree burn victims suffer serious fluid loss during and after a burn, through leakage from the circulatory system nourishing the skin. Large holes are generated in the dermis and hypodermis by a third-degree burn, with massive leakage occurring back into the surrounding tissue.
Skilled medical professionals working in burn centers may carefully remove cooled asphalt from the dermis in a sterile medical facility utilizing fat emulsifiers such as Neosporin ointments, mineral oil and even butter. The best solvents have a close structural affinity to the material being removed. While these methods are often more tolerated and less painful, they are often slow acting. Some recent medical studies have illustrated the merits of nontoxic polysorbate for removing tar from the wound, as it tends to chemically cleave the bond formed be-tween the exterior cells and the adhered material. It also tends to add surface lubricant to prevent skin drying. Debridement is another surgical procedure often required to remove dead skin tissue, which promotes bacterial growth from the burn, and to allow the new skin cells below to regenerate with ample oxygen supply. Depend-ing on the extent of the injuries and swelling, it may take several days for a physician to determine the need for skin graft procedures. In time there may be many cosmetic surgery options available for burn victims to recover from severe tissue destruction and scarring. Dangerous, post-burn secondary infections lead to many more ICU admissions than the initial burns themselves, as the protective external epidermal layer is destroyed first in a molten asphalt burn. Most burn physicians will closely monitor, sterilize and physically isolate the burn victim from bacterial exposures for weeks or even months, providing large prophylactic doses of antibiotics, until the risks for infection have been adequately minimized.
Burned skin regenerates with an uncommonly raised scarring pattern. Medically applied “pressure garments” can help the healing skin grow flat and protect the sensitive, regenerating nerve endings. Like any burn dress-ing, these garments need careful cleaning and attention. Physical therapy is always a feature of burn recovery. Although often excruciatingly painful, movement exercise helps reduce tissue swelling and improves overall health aiding the ability to recover.
Response at the SceneAs an excited, first responder to a serious burn victim, be very careful that you do not become likewise exposed to molten asphalt in your haste to help an injured co-worker. Two burn victims may increase the difficulty of providing prompt treatment many times more than one victim. Remember that chaos and panic are infectious conditions and events and must be prohibited by the competent person (CP) on site. If the incident is heading out of control of the CP, then all rescue operations should be suspended immediately and a clear-headed plan developed and implemented giving specific duties to each first responder involved. In the event of a molten as-phalt burn accident, the following first aid procedures should be followed:
- Call 911 immediately and inform responders of burn victim’s condition and location. Never hang up until directed to do so by the emergency response operator. Send a co-worker out to the main access road to guide emergency response team directly to the accident scene. Time is critical.
- Remove any tar-covered clothing, unless it is clearly adhered to the victim.
- Cool the asphalt and affected body parts immediately. Do not delay.
- Submerge area in ice water or cold running water. Do not hesitate. Use any available water cooler than body temperature while arranging for better cooling methods. (Note: Never apply ice directly to a burn.)
- Leave cooled, adhered asphalt in place for medical professionals to remove.
- Cautiously remove victim from hot-work area to prevent further burns. Be careful to avoid any contact with molten asphalt.
- Never attempt to remove the asphalt cement, unless it is mechanically impairing breathing or inhalation. Remove only enough to clear the airway.
- Never apply solvents or cleaning agents.
- If necessary in an emergency, soak bandage in mineral oil and place over area.
Natural dermal separation may occur within 48 to 72 hours. If the burn victim goes into shock, keep the victim lying down and as motionless and quiet as feasible. Cover victim with a blanket to keep body temperature nor-mal, and keep the head slightly lower than the feet, promoting blood flow to brain.
Asphalt Burn PreventionThere are a number of simple, commonsense steps the BUR crew can take to prevent the possibility of molten tar burns. I always recommend that the employer’s competent person should prepare a clipboard with a Job Safety Analysis (JSA) checklist in order to “observe, act and verify” any operations utilizing molten asphalt for hazard identification and control. Items to be included on the checklist for the kettle and application procedures are included below.
- All kettle operators should receive adequate initial and refresher training in safe kettle SOPs according to the employer’s site-specific safety and health program.
- The kettle operator shall not leave the kettle unattended or out of sight.
- Use a tanker to pump the product directly, avoiding kettle hazards entirely.
- Inspect the kettle thoroughly for any defects and damage pre-shift and pre-use.
- The kettle shall have a working temperature gauge.
- Shut down and tag out the kettle immediately when any condition exists which could affect the equipment’s safe operation.
- Burner fuels shall be limited to LPG, natural gas, fuel oil, kerosene or electricity. Gasoline may be used for pump motor only.
- Fuel tanks shall be located a minimum of 10 feet from the kettle or protected by a rigid, noncombustible material shield.
- Keep multiple 10-pound minimum (40-pound total) ABC dry chemical/CO extinguishers in place 10 to 25 feet from kettle. Extinguishers must be inspected and workers must be trained in proper method of use.
- The kettle shall be 20 feet minimum from combustible materials (10 feet overhead).
- The kettle shall have wheels chocked (both sides, all wheels) and should never be moved while being fired or while materials are molten.
- The kettle shall not be placed obstructing doorways, walkways or roadways.
- Kettle perimeter safety lines shall never be within a 45 degree angle from the top of any access ladder.
- The kettle shall be charged in a manner to avoid splashing; keg “splits” shall not exceed 25 pounds.
- Use a kettle designed with a safety feature such as the Safety Loader System™ by Reeves Equipment to prevent molten splash.
- Maintain the manufacturer’s operators manual on site at all times.
- Vessel shall not be filled closer than 6 inches from overflow.
- Always wear proper and adequate personal protective equipment, including:
- Safety glasses and face shield.
- Hardhat with Kevlar liner hood.
- Kevlar gloves.
- Leather steel-toed boots.
- Nomex™ or Dale™ flame-retardant, long sleeve shirt and pants (no synthetic materials, including underwear, should be worn).
- Appropriate, NIOSH-approved full-face filter respirator under the supervision of CP and in accordance with the employer’s respiratory protection program when asphalt fumes are potentially above the PEL (permissible exposure limit) in personal breathing zone.
- Maintain good housekeeping around the kettle to avoid any slips or trips. Promptly discharge any em-ployee from worksite who does not pick up after himself.
- Post Danger 360 degree warning line prohibiting entry into hazardous Controlled Access Zone (CAZ) by any unqualified personnel. Post clear hazard signage or monitor if necessary.
- Prohibit filling mop buckets directly from kettle (hot dip method).
- One trained, equipped first-aid responder shall be on the ground at all times (preferably not the kettle opera-tor, the most common victim).
Pump and Hot Pipe
- All employees must receive adequate initial and refresher training in safe pump/pipe SOPs according to employer’s site-specific SHP.
- Always inspect pump, pipe and fittings thoroughly for any defects and damage pre-shift and pre-use.
- Shut down pump operations and tag out equipment immediately when any condition exists which could affect the equipment’s safe operation.
- Maintain the manufacturer’s operators manual on site at all times.
- Regularly inspect pipe unions for leaks during pumping operations.
- Covered buckets should be used for vertical transfer of molten asphalt only when all other methods have proved infeasible.
- Filled mop buckets shall never be carried up a ladder or stair.
- Asphalt bucket hoisting shall be performed only by trained and experienced personnel under the super-vision of a CP.
- Leaking, defective buckets should be tagged “out-of-service” immediately.
- Tar buckets shall not be loaded closer than 2 inches from the top.
- Manual hoisting rigs shall have ¾-inch (minimum) manila (non-synthetic) hoist lines in good condition without mildew, burns, cuts or knots.
- Hooks with safety latches shall be used on all hoisted buckets (no knots).
- All components of a hoisting system shall have a safety factor of 4X.
- Workers shall never stand directly under overhead supported loads or within a 45 degree danger zone measured from highest point of hoist (12 feet high = 12 foot danger zone radius).
- Receive adequate initial and refresher training in safe lugger SOPs according to employer’s site-specific S&H Program.
- Adequate warning lines should be established around three sides of the lugger.
- Always wear adequate and proper PPE for hazards (JSA).
- All roofers shall wear long-sleeve shirts, long pants, leather boots and gloves.
- Always practice good housekeeping, eliminating roof deck debris and any other trip hazards.
- Asphalt spills are extremely slippery and should be mopped and covered with dry felt immedi-ately.
- Always keep 10-pound, inspected ABC dry chemical/CO extinguisher in place within 10 feet of the lugger, and train workers in proper method of use.
- During hot roof work, materials and equipment shall not be stored within 6 feet of the roof edge with-out guardrails, screen or netting being used.
- All materials stored less than 6 feet from the roof edge shall be stable and self- supporting.
- One trained, equipped first-aid responder shall be on the roof at all times.
Mopping and Spreading
- Receive adequate initial and refresher training in safe hot-mopping SOPs according to the employer’s site-specific S&H program. Always think before doing.
- Always wear adequate and proper PPE for identified hazards (JSA).
- Leaking, damaged buckets shall be tagged “out-of-service” immediately.
- Never over-fill mop buckets beyond the three-quarters level.
- Always practice good housekeeping and eliminate roof deck debris and trip hazards. Poor housekeep-ing practices are the No. 1 root causes of molten asphalt burns. Pay attention to your environment and your co-workers at all times.
- Always carry the bucket on the “downhill” side of your body.
- Always maintain a splash guard on the mop bucket.
- Place asphalt with a spreader whenever possible - avoid open mop-bucket accidents.
- Twist mops to unstick them from buckets; twist buckets to unstick them from deck.
- Hot mopping is a critically timed operation requiring skilled applicators and well-planned tactics. It does not require working faster than a walk. Running and “playing catch-up” are the No. 2 root causes of molten asphalt burns. Pay attention to your environment and your co-workers at all times.
Training is the Best DefenseWhile these safe work practices are recommended to prevent burn injuries on most BUR sites, they are just a starting point. As everyone who has read my columns must know by now, I am a prime advocate for compiling Job Safety Analyses from pre-bid through substantial completion. It is by this site-specific, task-specific and worker-specific evaluation form that we may best assess the actual hazards posed on a particu-lar job and the most effective engineering, administrative and PPE practices to control or eliminate them. A well-equipped BUR crew fully trained in a site-specific roof safety plan is the best defense against molten as-phalt burns. Hazard awareness levels in construction environments generally tend to decay as the days turn into months. Roofing is often classified as a “terminal task” in the critical path schedule of any building construction. Therefore, it is at this time when most of the workers on a multi-employer site have abandoned their self-awareness and supervision has become complacent in its site auditing responsibilities. The everyday hazards can become invisible, and the probability of being exposed to serious hazards created by someone else can increase exponentially.
While a concussion, contusion, laceration and even a broken bone are recoverable, the anatomical, physio-logical and psychological effects of a serious burn can be lifelong. Once tissue is contacted by molten as-phalt, the burn keeps on burning. While emergency burn treatment, reconstructive surgery and rehabilita-tion therapy are all critical parts of burn recovery, awareness is always the master key to burn prevention. Hazard avoidance is built upon equal parts hazard awareness and hazard mitigation. Take all the time, money and equipment you need to prepare your crews to avoid molten asphalt burns. Remember that every shift resulting in no burn injuries is another entry in the profit column for both you and your employees.