Where the Rubber Meets the Road
Approximately 176 tire fires occurred in the United States between 1971 and 1996 and many more could be added to this list after 1996. The environmental impacts associated with these fires were enormous. Consider the following tire fire events.
- 1998, Tracy, California - a tire fire burned for more than 28 days, consumed some 8,000,000 tires and released almost five million pounds of toxins - including 323,000 pounds of benzene.
- 1997, Gila River Indian Reservation in Arizona - fired burned 3,000,000 tires and lasted for 7 days.
- 1996, Philadelphia, Pennsylvania - an arsonist started a tire fire under I-95, burning 2,000,000 tires and destroying a portion of the expressway.
- 1995, Chautauqua County, New York - a fire burned for more than nine days, consuming some 6,000,000 tires.
- 1995, Midlothian, Texas - a fire at a recycling facility destroyed millions of tires during the 22 days it burned.
On average, each person in this country generates one waste tire every year and on an average more than 280 million waste tires each year. Some two to three billion scrap tires are in stockpiles and landfills across the nation. These waste tires represent approximately two percent of total solid waste generated in the United States.
What's in a typical 25 pound passenger car tire?
Texas has more than 100 waste tire stockpiles containing over 70,000,000 whole or shredded tires. The costs to extinguish and cleanup each of these sites, should they catch fire, are often in millions of dollars, an expense which is beyond the financial capability of most of the owners of these facilities. During the last five years, the U.S. Environmental Protection Agency (EPA) Region Six has spent over 3.5 million dollars responding to tire fires in the five-state region it covers (Texas, Louisiana, Arkansa, New Mexico and Oklahoma).
Although the percentage of tires recycled increased from the high teens in 1990 to more than 60 percent in the late 1990's, even then, the remaining percentage of these waste tires is a huge number that is either added to the existing piles or they are deposited in a landfill. More than 90 million un-recycled waste tires ends up in legal or illegal tire piles each year. Waste tire piles are also growing in major cities along the U.S./Mexico border.
How Scrap Tires Hurt the Environment
Waste tire dumps are an eyesore and whether legal or illegal, tire dumps can create a potential threat to human health and the environment. These waste tire piles present two major types of threats: disease vectors and fires.
The shape of the tire itself allows rainwater to accumulate and become stagnant. The stagnant water creates an ideal habitat for rats and a haven for breeding mosquitoes. These mosquitoes can carry deadly diseases, including LaCrosse Encephalitis, dengue fever, etc. In 1997, the U.S. Centers for Disease Control (CDC) reported a confirmed case of LaCrosse Encephalitis in Putnam County, West Virginia, near the Adkins Branch Tire Dump site. During that year, West Virginia alone had more reported cases of LaCrosse Encephalitis than the other 49 states combined.
The second major environmental threat presented by tire piles is an uncontrolled tire fire. Once a tire pile catches fire, whether via arson or by accident, it is very difficult to control. These fires create heavy air pollution and are resource exhausting. They are hard to extinguish and can burn for months, generating unhealthy, black, thick smoke loaded with toxins contaminating air, water and soil. A nasty oil-like by-product is also often released from the tires during a fire. Experience shows that for each 1,000,000 tires burning in an uncontrolled environment, approximately 55,000 gallons of this oily product is released.
The smoke from these fires releases more than 94 known chemical compounds including many metallic contaminants into the air. Thirty-two of the 94 compounds are toxic, such as poly-aromatic hydrocarbons (PAHs), benzene, styrene, butadiene, and phenol. About one-half of these are listed in the Clean Air Act (CAA) as air pollutants. The immediate concern is for people who might breathe toxic fumes released by burning tires. The elderly, as well as people with chronic heart and lung diseases, are more susceptible to the particulate matter. Besides particulate matter, the smoke also contains many respiratory irritants and may cause chest tightness or pain, repeated coughing, wheezing or whistling in the chest, difficulty breathing, headaches or nausea. The extent of evacuation that may occur during a tire fire event depends upon the vicinity of the population, wind direction and extent of the fire smoke.
Regulating Scrap Tires
There are no federal laws or regulations that specifically govern scrap tires. However, most states have been very active dealing with waste tires due to the potential disaster that might be created by improperly managed waste tire piles. Some of the common features of state regulations include:
- licensing or registration requirements of waste tire haulers, processors and storage sites;
- manifests for scrap tire shipment; and
- financial assurance requirements for processors.
Many states provide financial incentives to end-users in order to promote tire recycling. End-users have successfully recycled the waste thereby making it a useful commodity. EPA has promoted the policy and embraces a "waste reduction hierarchy" wherein the agency promotes:
- reduction of waste;
- reuse of products;
- recycling and buying of recycled products; and
- the disposal of used materials, but only as a last resort.
All efforts to conserve our precious, limited resources and to return them back into valuable goods and end-uses, thus avoiding their disposal for as long as possible should be made. States are utilizing many attractive alternatives to recover the natural contents from this huge waste resource.
Some Attractive End Uses
Tire derived fuel (TDF) is a waste-to-energy technology. TDF is a proven supplemental fuel for existing combustion units in several types of facilities. The TDF's use in existing units has been limited to blend ratios of 10 to 30 percent by British thermal units (BTU). A range of 13,000 to 15,000 BTU per pound of waste tire can be recovered, which is higher than both coal and wood. Use of TDF helps conserve precious natural resources and typically burns cleaner than coal. A dedicated boiler in the range of 500,000 #/hr steaming capacity would require approximately 66,000 scrap tires/day if converted to TDF to meet its fuel demand. According to the Scrap Tire Management Council (STMC), in 1998 approximately 114 million tires were used as TDF to save fossil fuel and recover energy from the waste. Cement kilns present the best option for TDF use, and whole tires could be used without any processing. Many paper mills and power plants also use TDF to supplement to their fossil fuels.
However, all boilers are not compatible with TDF use. Waste tire shredding may be required for boiler use, thus incurring additional cost compared to whole tire use. Boiler clumping and clogging are other common challenges to the use of TDF in many facilities.
Asphalt Rubber Pavements and Crumb Rubber Products
Crumb rubber is one of the most successful and proven options for used tire recycling. Crumb rubber has the potential for a very high diversion rate, particularly for asphalt rubber. Estimates show that 500 to 2,000 tires are used per lane-mile using rubberized asphalt. Furthermore, it has been shown that if only a small percentage of U.S. highways were re-paved using rubberized asphalt, it would be possible to use up all current scrap tires generated. Arizona uses more than almost 60% of its waste tires in asphalt rubber applications. California and Florida also actively utilize asphalt rubber on their roads.
Another major challenge with rubberized asphalt usage is the additional initial cost of using crumb rubber. The initial cost of high quality steel-free crumb rubber production is relatively high. Traditional concrete products generally have low initial cost (low initial cost but high O&M cost that makes high present worth). Increased research and education on proper application methods of asphalt rubber would result in reduced long range costs and better cost-to-benefit ratios. Reduced noise level, better durability and smooth ride are the added benefits of asphalt rubber roads.
There are many other uses of crumb rubber products. It can be used to produce athletic tracks, mats, carpet pads, and soil amendments, rather than using virgin resources in the production of these products.
Other Miscellaneous End Uses
There are many other environmentally friendly uses of waste tires that will conserve natural resources. Civil engineering projects to control soil erosion along highways and river banks and backfill with tires chips (50 percent mixed with soil) are good examples. An ambitious life cycle of a waste tire is presented in the following flow chart.
Becoming Better Stewards of this Product
Tire manufacturers, like manufacturers of other products, should consider the end use of the product at the design level. The tire manufacturers should design for durability and increased recycled content should be considered to reduce environmental impacts. Many efforts are being made at the design level. The State of North Carolina and Continental General Tire Company are engaged in a cooperative effort to manufacture tires with 25 percent recycled rubber
What is Product Stewartship?
Used tires can be retreaded to save the products, and they last just as long as new tires. Truck tires can be retreaded several times. Many states have both legislation and financial incentives to increase end use markets for products made from scrap tires.
Innovative Technologies on the Horizon
The Environmental Technologies Development and Commercialization Center at Sam Houston State University in Texas is currently collaborating with researchers. There are many promising technologies currently in the research or development phase.
- T-Rec technology consists of thermal reduction that converts the shredded tire into feedstock for methanol, fuel gas, etc. Products are rubber, black carbon, steel, etc. The process appears viable for demonstration.
- Pyrolysis (depolymerization) technology is conducted by feeding shredded tires to a pyrolysis chamber under air locks to control oxygen. Hydrocarbon vapors are generated that are then condensed in a further process into marketable products. The technology is suitable and essentially mature enough for demonstration and a patented process with a good demonstration history.
- Tire pyrolysis is a process in which tires are pyrolyzed in an indirect kiln at 500 degrees Celsius. Tire pieces are fed to a rotary kiln through an air locked feed system. Oil and other material is recovered from a vent gas stream that exits the kiln. About 30 percent of the tire weight is recovered as carbon, 12 percent as organic ash, 30 percent as oil, and the balance as gaseous material. The primary product is carbon black. The technology is suitable and essentially mature enough for demonstration.
- Ultrasonic devulcanization is a patented process in which ground rubber is placed in a reactor to conduct devulcanization. The technology, though apparently viable, is not currently mature enough for demonstration.
Waste tire piles are a growing challenge and are affecting the environment and public health. Managed properly to promote end uses such as TDF and asphalt rubber usage, the waste can be 100 percent recycled. Practice to reduce, reuse and recycle is the objective in resolving waste tire challenge in an environmentally friendly manner and only using the disposal option as a last resort.
To obtain any of the following documents, call the EPA RCRA, Superfund, and EPCRA Hotline at 800.424.9346; TDD 800.553.7672 (hearing impaired).
- 1997 Buy Recycled Series: Vehicular Products Air Emissions from Scrap Tire Combustion. EPA600-R-97-115.
- Analysis Of Ambient Monitoring Data In The Vicinity Of Open Tire Fires. EPA453-R-93-029. 1993.
- Environmental Fact Sheet: EPA Guideline for Purchasing Retread Tires. EPA530-SW-91-045. 1991.
- Environmental Fact Sheet: Purchasing and Maintaining Retread Passenger Tires. EPA530-F-95-019. 1995.
- Guideline For Federal Procurement of Retread Tires; Final Rule. EPA OSW-FR-90-005. 1988.
- Profile of the Rubber and Plastics Industry. EPA310-R-95-016. 1995.
- Project Summary: Characterization of Emissions from the Simulated Open Burning of Scrap Tires. EPA600-S2-89-054. 1990.
- Project Summary: Pilot-Scale Evaluation of the Potential for Emissions of Hazardous Air Pollutants from Combustion of Tire-Derived Fuels. EPA600-SR-94-070. 1994.
- State Scrap Tire Programs: Quick Reference Guide. EPA530-B-93-001. 1993.
- Summary of Markets for Scrap Tires. EPA530-SW-90-074B. 1991.
What's in a typical 25 pound passenger car tire?
- 14 percent natural rubber
- 27 percent synthetic rubber
- 28 percent carbon black
- 14 to 15 percent steel
- 16 to 17 percent fabric, accelerators, fillers
The average used tire weighs only 20 pounds.
What is Product Stewardship?
Product stewardship is a cooperative approach to sharing the responsibility and minimizing the impact on the environment adopted by all the players in the life cycle of a product. This is common practice in many states for products such as glass, aluminum, batteries, paper, etc.
This article originally appeared in the December 2001 issue of Environmental Protection, Vol. 12, No. 12, p. 26.
This article originally appeared in the 12/01/2001 issue of Environmental Protection.