It de-pressurises the bulbs and collects the dangerous mercury vapour in a carbon filter. The glass is pulverised into a granular form rather than creating dangerous shards.
The unit can take most common kinds of fluorescent lights including tubes, compact bulbs (the new household bulbs) and mercury vapour lamps. (These look like a glass football with a metal end cap and are often used in factories and shopping centres.)
It is designed to pre-process the bulbs safely on site so that less waste has to be transported to disposal stations and there is less risk of mercury leaking into the environment in transit.