How do I Insert the Gas Cartridge into my DDF5110500-DDF5120550 Gas Nailer? WARNING Injuries can occur due to accidental firing, ensure you remove the battery. Do not press the nose piece of the Gas Nailer against any surfaces. Keep your finger away from the trigger. Observe the safety instructions for the Gas Cartridge in the Instruction Manual Press the safety button on the cover/lid (1) and then open it (2). Remove the depleted gas cartridge (if present) and insert the new one. Close the lid again (locks into place).