On 2 July 2021, during pre-departure loading of a Boeing 777-300 at Heathrow prior to passenger boarding with only the operating crew on board, a rear hold fire warning was annunciated and smoke and fumes subsequently entered the passenger cabin. The Investigation found that the source was a refrigerated container which had been subject to abnormal external impact prior to or during loading causing a short circuit in its battery pack. The refrigeration system involved was found by design to inhibit fire following a short circuit but it was noted that QRH response procedures did not apply to the circumstances.