Most household waste recycling centres will accept fire extinguishers and some local authorities will accept them as a part of the regular houshold rubbish providing they are placed in 2 heavy duty plastic bags and placed with the rest of the bags of waste. Many companies which supply fire extinguishers will be happy to accept the extinguisher back so that they can refill it and reuse the device or they can arrange for its recycling using their own approved recycling routes.
