Both front seats are also fitted with a side impact protection system (SIPS) airbag which inflates in the event of a side impact to provide a cushion between the occupant and the door, reducing the risk of serious injury. Each seat assembly has a unit of sensors and a unit of air bags, with the sensor on the seat cushion frame and the airbag on the seat back frame, connected by tubes filled by combustible gas. The sensor is programmed to deploy the airbag only if the impact is significant, i.e. if the door impacts the seat at a speed of 2 m/s or more. In serious impacts, the sensor's cover deforms, setting off the ignition charge which inflates the airbag in milliseconds, creating protection before deflating almost immediately after impact. In the case of working on the front seats, it is very important that a protective tool is used over the SIPS sensor to avoid its accidental activation, by the care to access and fix it in place. From May 2000 onwards, the airbags in the front seats are integrated into a SIPS including side curtain airbags, with side impact sensors looking out for severe impacts. The side airbags deploy only on the side of impacted vehicle, and handling the later type front seats has less risk of triggering the airbags, although precautions should be taken when disconnecting the wiring. Side curtain airbags deploy from the panels in the roof during severe side impacts and prevent head or upper body injury to passengers and their presence must be taken into account when installing aftermarket equipment which may result in drilling in this area.