if knowing how and what to do, its perfectly safe.
another way to get the 18v, is to get a dunlop charge pump and connect to a 9v adaptor, it will provide 18v with the 9v adaptor. For more info, google dunlop charge pump. Can be gotten from blackwood if not wrong. For info of availability, look over to blackwood/ebenex forum or google their website for tele numbers to call.