Abstract: A starting device for a breathing apparatus employing chemically-fixed oxygen which incorporates a brick of oxygen generating material superposed by a resilient diaphragm giving support to an ampule with an ignition liquid. The ampule is broken by an ignition means located on the diaphragm under a gas-tight cap in an opening whereof there is provided a resilient bushing containing a removable detent arranged to interact with a retainer of the ignition means so as to keep same in a position ready for operation.