Cremation is the process of final disposition of the body in which the body is exposed to extreme heat for several hours which will vary according to the size of the body. Approximately 80Kg will burn per hour at 900 degrees Celsius. The body is reduced to its basic elements through this process, referred to as cremated remains. Cremation is carried out at a "Crematorium" in a special furnace called a retort. Bone fragments remain after the process and they are then mechanically processed to for ashes. Depending on the size of the body there are normally three to nine pounds of fragments resulting. These fragments are then mechanically processed in a separate machine to make the uniformed powder-like texture that many refer to “ashes”.
The “container” can range from a simple corrugated cardboard box to a solid wooden coffin. Many coffins are built from highly combustible materials to assist with the rapid cremation process but they may still contain non combustible external parts such as decorative handles, name plates or rails. These non-combustible fitting can damage the retort so will have to be removed by the operator before starting the cremation process.
Funeral homes may also offer a “rental coffins”. The purpose of these coffins are so that families can have a traditional looking casket for the service but will not incur the high costs. The rental casket will be driven to the crematorium in the hearse but once the service has completed the body will be transferred to another container for cremation. Rental coffins are sometimes designed with removable beds and liners that are replaced after each use.
As was said earlier a complete cremation is a two-step process. To begin the retort is heated to between 760 and 1150 °C (1400 to 2100 °F). Modern cremators are controlled by computers with interlocks and safety devices to ensure a legal and safe use. Only when the retort is heated to an ideal operating temperature will the door lock release for the body to be presented. To avoid heat loss from the open door the coffin is presented as quickly as possible. The body is then exposed to severe heat for around 1.5 – 2.5 hours depending on body mass.
The furnace can use a number of different fuel sources, such as natural gas or propane gas. Modern cremation furnaces include control systems that constantly monitor the conditions inside the retort. The operator can make subtle adjustments to provide more efficient burning as well as ensuring that minimal environmental pollution occurs. While the cremation is taking place, it may be necessary to open the cremation chamber and reposition the deceased in order to facilitate a complete and thorough cremation. In this process, a large part of the body (especially the organs) and other soft tissue is vaporized due to the heat and is discharged through the exhaust system.
The majority of the remains after the cremation process are bone fragments. These fragments represent about 5% of the body’s original mass. There will also be some ashes from the cardboard box or wooden container in addition to some metals (including dental gold and silver and other non-human material) as the temperature is not sufficient enough to consume them. These non-human materials make up a very small volume of the cremated remains
The remains are now swept from the retort by the operator and are placed into a machine called a cremulator (also known informally as a crembola). The cremulator grinds and crushes the bone fragments into a consistent powder. The cremulator is essentially a rotating drum similar to a tumble dryer, except it is fitted with steel ball bearing, which powders the weakened bones.
The cremated remains will be placed into a temporary container after completion of the actual cremation process. The crematory makes a reasonable effort to remove all of the cremated remains from the cremation chamber, but it is impossible to remove all of them, as some dust and other residue from the process might be left behind. All non-combustible and non-human materials will be separated from the cremated remains.