Cremation is the process of reducing human remains to a small amount of non-combustible material, generally a few pounds of bone fragments referred to as "ashes." In many cultures, cremation is commonly used as an alternative to burial or as a primary means of body disposition. Modern cremation is a complex and highly specialized procedure requiring high levels of heat for a considerable period of time, and is carried out using purpose-designed crematoriums.
Preparation of the Remains
Before a deceased person is cremated, certain steps must be taken to prepare the body. If the family held a public viewing as part of the memorial service, the deceased person is dressed in the funeral clothes. If any jewelry or other items present at the service are not to be cremated, they are removed at this time. Certain implants, such as pacemakers, must also be removed from the body before cremation, to avoid explosions. Dental fillings and surgical pins are not removed. Often, a metal identity tag is attached to the person to ensure that the remains can be identified after cremation.
Placing the Remains in the Furnace
The deceased person is placed inside the furnace while the furnace is cool. Only one person may be cremated at a time, although some larger furnaces may have multiple chambers. The deceased person is often inside a casket, although in some states it is allowable to cremate a person without any sort of container. The deceased person is placed in the center of the furnace and the door is secured.
Cremating the Remains
When the furnace is activated, a superheated jet of flame is introduced to the chamber, quickly raising the internal heat to 1800°F-2000°F (982°C-1093°C). Over the course of two hours, all combustible material in the body is burned away, as is the container. The process may take longer for older or less efficient furnaces. Once the process is complete, nothing is left in the furnace but bone fragments.
Processing the Cremated Remains
The furnace takes about a half hour to an hour to cool. Once it has cooled to a safe level, the furnace is opened and the bone fragments are carefully collected. Any metal surgical appliances, such as titanium pins or rods, are separated out at this point. The bones fragments are then ground into a coarse white powder and placed in a container to be delivered to the family. This may be an unadorned plastic container or an urn provided by the family.