The following section provides information about work practices, engineering control methods, and personal protective equipment (PPE) that can be effective in reducing worker exposure to asphalt fumes at the kettle and during the application of hot asphalt to roofs. This information is presented according to the order of preference in the occupational safety and health hierarchy of controls [NSC 1996]. They range from control methods and work practices that can be followed on any roofing operation to those that reflect recently emerging approaches and technologies.

5.1 SUBSTITUTING LOW-FUMING ASPHALT

Low-fuming asphalt (i.e., the addition of small amounts of polymer to the asphalt) has been developed to reduce the emission of asphalt fumes from the kettle. Some of the polymer separates from the asphalt and forms a floating skim on the surface of the asphalt in the kettle. Results from initial field studies indicate that the skim formed on the surface of the asphalt dramatically reduces fume emissions and subsequently worker exposures [Franzen and Trumbore 2000]. According to one manufacturer, this technology works with any asphalt in any kettle and has no impact on product performance [Trumbore 2000].

The materials tested to date included asphalts containing polymer (either polypropylene or a blend of polypropylene and ethylene vinyl acetate copolymer) in amounts that are 0.3% to 1% of the asphalt by weight [Franzen and Trumbore 2000]. The polymer is either contained in the packaging material (meltable) that surrounds the asphalt keg or introduced during manufacturing of the roofing asphalt.

Studies in a controlled pilot plant setting showed average reduction in asphalt fume emissions (measured by high-volume-area samplers positioned directly above the kettle) of 89% for total particulates and 92% for benzene solubles [Franzen and Trumbore 2000]. PBZ exposures of a kettle operator were reduced by 84%, measured as benzene solubles. In addition, the use of the low-fuming asphalt negated the significant emission-increasing effects of higher temperatures that characterize conventional roofing asphalts.

The results of ongoing field investigations conducted in concert with NIOSH have thus far confirmed the pilot plant studies. The results to date show 70% to 88% reductions in asphalt fume emissions and 80% to 90% reductions in PBZ exposures of kettle operators [Franzen and Trumbore 2000]. In addition, recent unpublished data suggest that use of a low-fuming asphalt may reduce asphalt fume exposure to rooftop workers [Owens Corning 2000].

5.2 KETTLE SELECTION

Job-planning, setup, and advance worksite preparation are important considerations in minimizing worker exposure to asphalt fumes. The appropriate size of kettle should be selected to meet the demands of the job. Use of a kettle with inadequate capacity for the job will require the lid to be opened more frequently than necessary to ensure adequate quantities of heated asphalt to support the roofing work. Frequent opening of the lid will result in (1) more frequent worker exposure to asphalt fumes, (2) inconsistent asphalt temperatures that affect the application and quality of the asphalt, and (3) the need to heat the asphalt to unnecessarily high temperatures. For some jobs, it may be appropriate to use the tanker that delivers the asphalt instead of a kettle. The use of a tanker instead of a kettle can reduce fume emissions for jobs in which a large quantity of asphalt is used.

5.3 STEPS TO ISOLATE THE PROCESS AND MINIMIZE GENERATION OF FUMES

5.3.1 Placing the Kettle at the Worksite

The location of the kettle can have a significant effect on asphalt fume exposures to workers. When placing the kettle, take the following steps:

1. Minimize the distance from the kettle to the rooftop and use an insulated hot pipe to transfer the hot asphalt to the roof and avoid an unnecessary increase in the asphalt temperature at the kettle.

2. Set the kettle on level ground to avoid spilling asphalt or tipping over the kettle.

3. Place the kettle where the operator and other workers will be least exposed to the fumes—for example, downwind from the workers.

Regardless of location, the kettle should always be positioned with the inside of the lid facing away from the building (so that fume emissions are released away from the building when the lid is open).

The kettle should also be placed to minimize the risk of exposing building occupants to asphalt fumes. Therefore, place the kettle away from air intake vents, doors, and windows. Note also that some local fire safety codes may require the kettle to be located a minimum distance away from building walls and/or other combustible surfaces. Always check with the building manager to ensure that the air intake system is off and that covering the intakes will not cause damage to the ventilation system. If possible, work during off hours and give the building occupants a few days of notice before starting the job. Close and cover all building air intakes.

Because the kettle is the major source of asphalt fume exposure, restrict access to the area immediately surrounding the kettle. Mark the area with warning tape, traffic cones, and/or signs. The restricted area should be large enough to keep the public away from contact with the kettle or the asphalt and to allow sufficient space for the kettle operator to work. Restricting access also reduces the risk of burns to workers and bystanders and makes it less likely that vehicles or other equipment will unintentionally be permitted into the area.

5.3.2 Maintaining Asphalt Temperature in the Kettle

The following work practices and fume reduction techniques at the kettle are important for (1) maintaining the asphalt at the desired temperature for application, (2) reducing the risk of fires and explosions, and (3) minimizing fume generation and worker exposure. Also, asphalt kettles should have tight-fitting lids and should be closed during normal operations when asphalt is not being loaded.

To ensure reasonably accurate asphalt temperature readings at the kettle, follow these work practices:

As a generally accepted practice, the kettle temperature should initially be set at 50 ?F (28 ?C) above the EVT and then adjusted as needed to ensure that the EVT is maintained at the point of application on the roof. However, the kettle temperature should be kept at least 25 ?F (14 ?C) below the flash point temperature at all times. Maintaining the lowest possible asphalt temperature in the kettle will reduce the amount of fume generated and have quality benefits in reduced fallback and reduced coke/carbon buildup in the kettle.

When opening the kettle lid to refill the kettle, fill it to the maximum recommended fluid level. The kettle operator should chop asphalt kegs into manageable pieces before the refill operation to shorten the time needed to have the kettle lid open during refilling. These steps will help to maintain a constant asphalt temperature in the kettle, minimize the release of asphalt fumes, and reduce fume exposure to the kettle operator and other workers.

5.3.3 Applying Asphalt on the Roof

Many of the rooftop machines used to transport and apply the hot asphalt can also be insulated or covered, thereby reducing heat loss as well as the emission of asphalt fumes. Hot luggers, used to transport hot asphalt from the supply line to the area of application, typically have a capacity of 55 gal and can be insulated and covered. During this transfer from the hot lugger, using the draw-off valve/spigot at the proper height will help to avoid splash hazards and reduce heat loss. Felt-laying machines also carry a substantial reservoir of hot asphalt (typically, 40 to 49 gal), and some are insulated with lid covers. However, it is impractical to cover mop carts used for hot mop application of the asphalt, since the mop must constantly be moved in and out of the hot asphalt.

Workers applying hot asphalt on the roof should work upwind whenever possible to reduce their exposure to asphalt fumes. Operations involving filling or refilling of hot luggers, mop carts, buckets, and other containers of asphalt (such as those on mechanical asphalt spreaders or felt-laying machines) should also be conducted while standing immediately upwind of the operation whenever possible. Any lids or covers on containers of hot asphalt (such as those on hot luggers, mechanical spreaders, or felt-laying machines) should remain closed except during refilling operations. Buckets of hot asphalt should be no more than three-quarters full and should have half lids to reduce spillage. Workers should carry buckets on the down-roof side, and they should always use a twisting motion to unstick buckets and mops. For work in partially confined or poorly ventilated spaces (such as under eaves), fans may be an effective way to circulate the asphalt fumes away from the work area. If fans are used, they should be grounded and kept out of walking paths and any areas where contact with hot asphalt or liquids may occur.

5.4 CONTROL DEVICES FOR REDUCING ASPHALT FUME EMISSIONS

Asphalt fume emissions from the kettle can be reduced by maintaining a constant asphalt temperature in the kettle and preventing the release of fumes by the use of various control methods. A variety of thermostatically controlled heating systems are available to maintain a set asphalt temperature in the kettle. In addition, kettles are often constructed of double walls with thermal insulation between the walls; they may also have double lids to help maintain a constant temperature. Pumping rates have also increased substantially and are now typically 60 gal/min compared with 35 gal/min in the 1970s. This higher pumping rate reduces heat loss between the kettle and the point of application.
Using insulation throughout the mechanical systems that transport the liquid asphalt from the kettle to the point of application will reduce the amount of heat lost and thereby allow the kettle to be operated at lower temperatures. Pipe-insulating materials include fibrous supply line insulation and high-temperature glass fiber insulation. Since the pipe-insulating materials also help maintain the asphalt temperature in the pipe, they also reduce clogging of the supply lines caused by cooling and solidifying the asphalt on the inside walls of the pipe.

Several types of emission control devices (including emission capture and destruction devices as well as load insertion devices) have been introduced for use on kettles to reduce fume exposure. Emission capture and destruction devices consist of a vent or exhaust system that evacuates fumes from the headspace inside the kettle to a capture or destruction device. These devices often include afterburners, reburners, filters, and condensation systems. Most of these systems draw fumes from the headspace inside the kettle, thereby reducing the concentration of asphalt fumes inside the headspace. However, if the asphalt in the kettle is at a temperature that generates sufficient combustible vapors to exceed the UEL, these emission control systems may inadvertently lower the concentration of the asphalt fumes into the explosive range. Therefore, appropriate control devices are needed to monitor and maintain the asphalt fume concentration in the kettle headspace below the LEL. Also, steps need to be taken to prevent the airflow from causing coke to smolder and become an ignition source in the kettle headspace.

Controls (i.e., damper/flue) designed to regulate the airflow are being evaluated. In the meantime, prevent the potential for creating an explosion and fire risk by avoiding overheating of the asphalt, keeping the asphalt fume concentration in the headspace of the kettle below the LEL, and eliminating ignition sources.

Some afterburner systems use an open flame that can act as an ignition source. The ignition risk associated with the afterburner can be reduced by using flame arrestors, but these are prone to clogging and may not be sufficiently reliable to work effectively under actual operating conditions.

Another potential problem is coke or carbon buildup on the firewall of the kettle resulting from overheating of the asphalt. When a kettle is operated at high temperatures, this buildup can become so hot that it will glow red and act as an additional ignition source.

In systems that do not use afterburners or reburners, other potential ignition sources include the heating tube vent stack or flue. Kettle heating tubes generally run lengthwise through the vessel, then they turn and pass vertically through the kettle headspace to vent above the top deck of the kettle. In some situations, the asphalt itself can become an ignition source (i.e., if the asphalt temperature reaches at least 600 ?F [316 ?C]).

In addition to incineration, another method of reducing asphalt fume emissions is filtration. This newly emerging technology uses a series of filters, including high-efficiency particulate air (HEPA) filters and activated carbon to capture and filter particulates and vapors from the asphalt fume.

Loading devices provide another means of reducing the emission of asphalt fumes from the kettle. These devices allow the kettle operator to refill the kettle without opening the lid. Designs include mail slot openings and rotating loading drums that drop the solid asphalt into the kettle. Since all of these devices must be located above the liquid level in the kettle, they increase the headspace above the liquid asphalt. Although increasing the headspace in the kettle does not necessarily increase the risk of explosion, it can significantly increase the size of the explosion. In addition, these devices effectively reduce the usable capacity of the kettle. This reduction may create an incentive to overheat the asphalt in some circumstances, such as when the kettle operator needs to melt the asphalt more quickly to meet the needs of the rooftop crew for hot asphalt. Another difficulty with loading devices may arise from the inability of the kettle operator to evenly distribute the new asphalt as it is added to the hot asphalt already in the kettle. This situation can lead to “pyramiding” of the newly introduced (cold) asphalt in the kettle’s heating vessel. Pyramiding may cause the loading device to operate incorrectly and may also create “cold spots” that could cause the kettle thermostat to heat the asphalt to excessively high temperatures. If not maintained properly, loading devices can also become clogged, necessitating the opening of the kettle lid so that the solid chunks of asphalt can be moved out of the way of the loading door. The opening of the kettle lid allows the release of additional asphalt fume into the work environment.

5.5 TRAINING AND EDUCATION

Workers should be trained in the use of good work practices for reducing exposure to asphalt fumes. They should also be provided with appropriate educational materials informing them of the potential hazards associated with working with asphalt.

5.6 USE OF PPE

5.6.1 Personal Protective Clothing and Gear

Proper PPE includes cuffless long pants and long-sleeved shirts made from natural fibers (avoid manmade organics such as polyester), nonskid shoes or boots with leather uppers that cover the ankles, safety glasses with side shields or goggles for rooftop workers whose eyes are sensitive to the fumes, face shields for kettle operators, and hard hats and leather gloves for all workers. Wearing PPE primarily protects workers against the risk of asphalt burns, but it can also reduce dermal contact with asphalt and asphalt fumes.

5.6.2 Respiratory Protection

Respirator use may be called for if available engineering controls and work practices are ineffective in controlling asphalt fume exposures to concentrations below the NIOSH REL of 5 mg/m3 (total particulates measured as a 15-min ceiling) or applicable State or Federal standards. However, because respirator use can introduce new safety hazards in roofing work, respirator use should be the last resort for controlling exposures. When respiratory protection is provided, all applicable OSHA requirements should be followed in accordance with a written respirator program, including the use of NIOSH-approved respirators (see Appendix B), training, fit-testing, medical approval, and proper inspection, cleaning, maintenance, repair, and storage of respirators [29 CFR* 1910.134].