Two questions:
1. How long will this take to re-pack and get signed off?
2. Why on earth is a fire engine on the scene?
1. They should have a spare as it's at LHR so it's just a case of dismantling that one and fitting another. Still a couple of hours or so though. If they have a spare aircraft it may be quicker to just use that one for the flight. That slide will be sent to Cardiff to be checked and repacked.
2. Precautions.