Because they trap air, which increases their buoyancy, they rise to the surface and break through landfill covers. These covers are made of materials that are designed to seal off the contained wastes from rainwater and runoff. The leachate created when water percolates thorough the landfill can harm surface and groundwater. When tires stored in piles heat up, they turn into a liquid petroleum product, which is highly flammable. Such fires can have far-reaching effects on public safety and the environment, including contamination of surface water, groundwater, air, and soil.
Tire fires can produce benzene, a known carcinogen.
Tire fires also can require up to 100 gallons of water per tire to suppress, which creates additional environmental problems such as hazardous waste runoff. Often the best course of action for firefighters is to let the fire burn itself out, but this can take weeks or months. Several tire fires have involved millions of tires. The stockpiled tires also collect water and can be breeding grounds for mosquitoes and vermin. Finally, they are objectionable on aesthetic grounds.