Modern municipal incinerator designs include a high-temperature zone, where the flue gas is sustained at a temperature above for at least 2 seconds before it is cooled down. They are equipped with auxiliary heaters to ensure this at all times. These are often fueled by oil or natural gas, and are normally only active for a very small fraction of the time. Further, most modern incinerators utilize fabric filters (often with Teflon membranes to enhance collection of sub-micron particles) which can capture dioxins present in or on solid particles.