Hydrogen in bottles at high pressure is stored at the top of the bus and in this vehicle there will be zero pollution since the product of cold combustion is water. The hydrogen cells were a spin-off of the cryogenic technology. ISRO has developed a rich technology in producing, storing and handling gaseous and liquid hydrogen in the last three decades and which is quite safe indeed.
ISRO, Tata Motors develop India's first Hydrogen powered cell bus
Month: Current Affairs - July, 2013