Geysers are known to burst when there is excess of water / steam pressure. This can be caused due to two major reason.
1) High water pressure above the rated capacity of your inner tank.
2) The thermostat is incorrectly set or badly regulated as it will incorrectly control the heat levels of the water in the geyser and possibly cause an explosion due to the amount of steam that accumulates.
In high rise building Specially In Mumbai, the water pressure needs to be controlled with the help Pressure Reducing Valve (PRV). On an average Max pressure withstanding capacity of a storage water heater is 8 Bar. So it is advisable to use a PRV which can reduce the pressure between 4-6 bar.
All major company in India have equipped Storage water heaters with a Mechanical Attachment know as Multi-Function Valve (MFV) / Safety Valve. To avoid Bursting of inner tank this MFV is very useful. It has a venting system which lets the excess pressure release in the overflow pipe. Thus avoiding excess pressure building up in inner tank preventing it from bursting.
Under thermostat failure there is chances of heater plate gasket, heating element gasket overheating resulting in melting of the gasket. Resulting in leakage. Always allow only trained Geyser technician to adjust the thermostat Setting and insist on using of original Spare parts for your respective Brand Geyser.