Hydrogen fuel cells promise to break the world’s fossil fuel habit without a puff of carbon dioxide, and Joseph Cargnelli is helping them deliver. In 1995,from a small room above his family’s machine shop in Toronto, Ontario, the mechanical engineer and two associates launched Hydrogenics. The company made its mark producing test stations Cargnelli designed and assembled to put fuel cells through their paces. The test units accelerated the work of fuel cell developers and secured Hydrogenics’$84 million initial public offering in 2000.Today Cargnelli, vice president, is worth millions. But the roar of equipment still fills his shop floor office at a complex on Toronto’s west side, where Hydrogenics is developing its own fuel cell engines. Last year,in a six-month span, Cargnelli’s team prototyped a fuel cell generator and transformed it into a backup power supply to keep cell tower antennas and their networks alive during blackouts. This work clinched a partnership with General Motors. To Cargnelli, success just means one more step toward the hydrogen economy.