Cremation - Modern Cremation Process

Modern Cremation Process

The cremation occurs in a crematory that is housed within a crematorium and comprises one or more furnaces. A cremator is an industrial furnace that is able to generate temperatures of 870–980 °C (1600–1800 °F) to ensure disintegration of the corpse. A crematorium may be part of a chapel or a funeral home or may be an independent facility or a service offered by a cemetery.

Modern cremator fuels include oil, natural gas, propane, and, in some areas like Hong Kong, town gas. However, coal and coke were used until the early 1960s.

Modern cremators have adjustable-control systems that monitor the furnace during cremation. These systems automatically monitor the interior to tell when the cremation process is complete, after which the furnace automatically shuts down. The time required for cremation varies from body to body, and, in modern furnaces, the process may be as fast as one hour per 45 kg (100 lb) of body weight.

A cremator is not designed to cremate more than one human body at a time; cremation of multiple bodies is illegal in the United States and many other countries. Exceptions may be made in special cases, such as with still-born twins or with a still-born baby and a mother who died during childbirth. In such cases, the bodies must be cremated in the same container.

The chamber where the body is placed is called a retort and is lined with heat-resistant refractory bricks. Refractory bricks are designed in several layers. The outer most layer is usually simply an insulation material, e.g., mineral wool. Inside is typically a layer of insulation brick, mostly calcium silicate in nature. Heavy duty cremators are usually designed with two layers of fire bricks inside the insulation layer. The layer of fire bricks in contact with the combustion process protects the outer layer and is required to be replaced from time to time. The coffin or container is inserted (charged) into the retort as quickly as possible to avoid heat loss through the top door. The container may be mounted on a charger (motorised trolley) that can quickly insert it, or on a fixed or movable hopper that allows the container to slide into the cremator.

Modern cremators are computer-controlled to ensure legal and safe use. For example, the retort door cannot be opened until the cremator has reached its operating temperature, and United States federal regulations require that newly constructed cremators feature dual electrical and mechanical heat-shutoff switches and door releases that are accessible from inside the retort. Refractory bricks are typically replaced every five years, because thermal fatigue gradually introduces fissures that reduce the insulating strength. For heavy duty cremators having an inner sacrificial layer of refractory material, often cracks, slagging, bulging and dislocation can be seen on this layer shortly after the cremator is put into use. Such cracks and fracture need not be disastrous, as this lining is sacrificial in nature — it may just result in the development of a crack pattern in the lining. Those crack surfaces may be held together and closed by the lining compressive stresses that develop from thermal expansion when the cremator is heated to operating temperatures. However, the inner sacrificial lining needs to be replaced on a regular basis to offer proper protection to the outer layers.

Some crematoria allow relatives to view the charging. This is sometimes done for religious reasons, such as in traditional Hindu and Jain funerals.

The size of most cremators is standardized. Typically, larger cities have access to an oversized cremator that can handle corpse in the 200 kilograms (440 lb)+ range. Most large crematoria have small cremators installed for the cremation of fetal and infant remains.