High voltage relays are used to transfer power for high voltage and high frequency applications. They are heavily insulated and consist of strong materials to increase contact life. High voltage relays use several isolation methods to achieve high dielectric strength. Some devices include a vacuum to produce the greatest possible isolation between contact electrodes. Others contain specialized or proprietary gas mixtures at several atmospheres of pressure. High voltage relays that contain fluids such as oil are commonly available. Other isolation methods use reed relays or air as the dielectric. Hermetically sealed devices feature an airtight seal that prevents contamination. Intrinsically safe (IS) relays are incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous mixture in its most ignited concentration.