I've learned a bit about cremating dead bodies this week, since my father was cremated. Here is some information that I lifted from the
Everlife Memorials website:
The funeral director must remove any items not wished to be cremated along with the body such as jewelry. If the deceased had a pacemaker or other type of medical device, it too will need to be removed to prevent an explosion from occurring during the cremation process.
The body is then placed in a cremation casket, usually made of wood, or more often a cremation container which is basically a large cardboard box with a plywood bottom for sturdiness. These types of containers will burn fairly well during the cremation cycle.
The funeral director or crematory operator will place an identification tag in the cremation container with the body to properly identify the cremated remains once returned to the funeral home. This is a very important step as it insures the family does not end up with the wrong set of cremated ashes.
The cremation container/casket containing the body is then placed in the cremation chamber from the end. The cremation chamber is lined with fire resistant bricks on the walls and ceiling. The floor is made from a special masonry compound formulated specifically to withstand extremely high temperatures. Once the body is in, the chamber door, which is about a half a foot thick, is closed either by hand or in some cases a switch as many of the newer models have automated doors.
The crematory operator then starts the machine which normally goes through a warm up cycle before the main burning begins. After the machine is warmed up, the main burner ignites starting the process of incinerating the body. Temperatures within the chamber often reach the 1800°F - 2000°F range. The burners within a cremator are fueled by either natural gas or propane.
It generally takes about 1-1/2 to 2 hours for a body to be completely reduced to just the bone fragments by cremation. Some cremation furnaces, especially the older ones, may require a little more time.
After the entire incinerating process is complete, a cool down period of 30 minutes to an hour is required before the bone fragments can be handled for further processing. When the time finally arrives, the cremated remains or bone fragments are removed from the cremation chamber and placed on a table work area. It is here that the crematory operator removes all metal debris such as screws, nails, surgical pins or titanium limbs/joints with a magnet and by hand.
The remaining bone fragments are then placed in a special processor which is kind of like a cross between a disposal unit from under a kitchen sink and a blender. This processor pulverizes the bone fragments to a fine powder called cremains or more commonly referred to as the ashes.
The ashes are then placed in a plastic bag within a temporary cremation container or an urn provided one is furnished to the crematory.