A method of sterilisation, sanitisation and/or decontamination comprises the steps of producing a humidified environment having a relative humidity corresponding to a partial pressure of water vapour that is higher than 5.00 torr； discharging ozone into the humidified environment； maintaining the ozone level at a concentration that will achieve the required degree of decontamination and sterilisation of the humid environment； reducing the concentration of ozone in the decontamination and/or sterilised environment to a predetermined level, preferably by passing the environment through a catalyst or photochemical device； introducing a hydrocarbon containing a carbon-carbon double bond into the environment to react preferentially with the discharged ozone； and, optionally, recycling the decontaminated and sterilised environment through the catalyst until the concentration of harmful byproducts falls to a safe level. The ozone level is reduced by introducing a hydrocarbon containing a carbon-carbon double bond, such as an alkene or a cyclo-alkene to the environment. Apparatus for carrying out the method is also claimed.
