As the car seat swings back and then forwards, the child sitting in it is flung out of his harness and his head hits the seat in front. The accident is one that would make any parent sick with fear.
Luckily, this is not a real accident, but a mock crash staged by the Transport Research Laboratory for The Observer. Using a dummy, it shows – all too graphically – the shocking results of strapping a child into a badly fitted car seat.
In this test, the seat belt fixing the seat in place has been mis-routed, the headrest has been removed and the harness is slightly too slack – all common errors parents make when fitting the seats.
The impacts could result in serious head injuries, as well as damage to limbs, according to TRL's head of child safety, Marianne Hynd.
As part of our campaign to stop children being put at risk of unnecessary injuries, we wanted to find out what impact common fitting mistakes could have in the event of a crash.
Accident investigators do not collect data on whether child seats are correctly fitted, and crash tests usually focus on those that are, so our tests give a rare insight into what can happen if a misused seat is involved in an accident.
The results are harrowing. In a video of the tests, a dummy in a badly fitted rear-facing group 0+ seat is thrown backwards after a front impact, and in one test even comes free of the harness before being thrown against the backseat.
"For children travelling in rearward facing infant carriers, the most frequent injury is to the head. These typically happen in front impacts when either the child or the child seat hits the vehicle dashboard and if the child rebounds on to the vehicle structure," says Hynd.
"In the test where the adult belt was attached incorrectly around the seat, the seat travelled much further forward ... if this seat had been in a car, it is likely that it would have hit the dashboard or the vehicle structure."
TRL has carried out child safety research for the Department for Transport for more than 30 years, and analysed accidents which have resulted in fatalities and serious injuries.
It ran our tests using the same equipment, and to the same standards, as those used by manufacturers hoping to meet United Nations ECE regulation 44 – the standard legally required to sell car seats within the UK.
As in those tests, a sled fixed to a track was used, and a front impact crash at 48kph (c30mph) simulated.
In the first test, the seat was fitted correctly; in two subsequent tests it was incorrectly fitted. The fitting mistakes were similar to those seen by road safety officers in checks around the country, including a mis-routed seatbelt, loose harness and seatbelt, and the removal of the child's head support.
The first test revealed that even a relatively cheap seat can offer protection. In that simulated accident the seat, which cost around £30 from Argos, cocoons the test dummy. As the seat is thrown against the back seat of the car, the handle, which is in the correct upright position, acts as a roll bar. Because the harness has been tightened properly, the baby remains strapped in.
In the second test, the seatbelt was mis-routed and the head support removed (a mistake one tester had seen a relative make). The harness inside the seat was loosened, as though to make room for a child wearing a coat or snow suit. The seat felt fairly stable when shaken.
The handle was also put back. At the point of impact, the seatbelt retained the seat, but the dummy was thrown forward, putting serious strain on its neck. For the third test, the seatbelt and harness were slackened further, resulting in more movement after impact, and the dummy eventually being thrown out of the harness and against the backseat.
Hynd, who works as an adviser on car seats to the European Commission and represents the UK on working groups for child seat safety, said this would have resulted in head injuries.
She said the slackness of the harness would have prevented the seat spreading the force of the crash over the child's body and reducing injury. "Too much slack in the harness means that the child will be caught later in the crash, because the harness doesn't have time to absorb the energy," she said. In some cases, it can even result in the child being ejected.
Hynd added that, in a real crash, the car would pitch forward and that movement could be enough to send the car seat into the footwell.
Anyone concerned about their car seat should contact their council's road safety department to see if they offer fitting checks, or visit our website for details of where to get more information.
The TRL is running a ratings system for seats which factors in how easy the seats are to install. So far, only three manufacturers have put seats forward to be rated.