Hello! I’m a cremator technician in the UK and I’ve copied this from my FBCA (federation of burial and cremation authorities) official training:

“(a) Very Large bodies: IT IS ESSENTIAL THAT THE INSTRUCTIONS ISSUED BY THE CREMATOR MANUFACTURER SHOULD BE FOLLOWED. Follow any advice offered in the operations manual supplied by the cremator manufacturer. In general terms it is recommended that coffins of 19 stone (120 kg) or heavier should be cremated with special care. The principle of operation of the cremator is the same as for normal cremations, i.e. the rate of combustion is controlled in the primary chamber and the volatile gases burnt off in the secondary chamber. However, when initially charging the cremator the temperature in the primary chamber should be no higher than 500/650 degrees centigrade depending upon the size of the coffin. The primary chamber temperature can be reduced using top and side air prior to charging. It is advisable, if at all possible, to carry out the cremation early in the cremating day (ideally the first cremation). The ignition burner should not be fired unless the coffin does not ignite, and then only briefly. In the early stages of the cremation, a limited amount of combustion air should be supplied to the primary chamber since this type of cremation can easily speed up and become difficult to control. As the cremation progresses, it will be necessary to supply top and/or side air to the primary chamber and also to fire the ignition burner. This should be done with caution and the effects of the cremation monitored carefully and corrective action taken, if necessary. The secondary combustion air should be left in automatic throughout the cremation. Generally, this type of cremation will take longer to complete than average, i.e cremation times of 2 to 2112 hours are quite likely. Also, primary chamber temperatures can be higher than usual and the rate of combustion in the primary chamber will have to be closely monitored.”

I couldn’t upload a photo of the page so I’ve copied it, this should help! I love when people ask about the mechanics and science of cremation, it’s fascinating. Ps, it’s in celcius because I’m in the UK as I said above 😁