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A crematory (also known as a crematorium, cremator or retort) is a machine in which cremation takes place. Crematories are usually found in funeral homes, chapels, cemeteries, or in stand-alone facilities. A facility which houses the actual cremator units is referred to as a crematorium.
Prior to the Industrial Revolution, any cremation which took place was on an outdoor, open pyre. With firewood, and to a lesser extent, coal being the only available fuel options and the low energy efficiency inherent in such a configuration, it is no surprise that cremation enjoyed minimal popularity in densely populated areas up until furnace technology developed during the Industrial Revolution could be applied to cremation to make it more practical in an urbanizing world.
The first modern crematory 
In 1873, Paduan Professor Brunetti presented a cremation chamber at the Vienna Exposition. In Britain, the movement found the support of Queen Victoria's surgeon, Sir Henry Thompson, who together with colleagues founded the Cremation Society of England in 1874. The first crematoria in Europe were built in 1878 in Woking, Surrey, England (see Woking Crematorium) and Gotha, Germany, the first in North America, the LeMoyne Crematory, in 1876 by Dr. Francis Julius LeMoyne in Washington, Pennsylvania. The second cremation in the United States was that of Charles F. Winslow in Salt Lake City, Utah on 31 July 1877. The first cremation in Britain took place on 26 March 1886 at Woking. Newer crematories now have a feature called 'hot hearth crematory' which is a two-chamber technology which allows the body to burn in the upper chamber while the lower chamber allows heat to be carried through the bottom to keep the top chamber hot.
Cremation was declared as legal in England and Wales when Dr. William Price was prosecuted for cremating his son; formal legislation followed later with the passing of the Cremation Act of 1902 (this Act did not extend to Ireland), which imposed procedural requirements before a cremation could occur and restricted the practice to authorised places. Some of the various Protestant churches came to accept cremation, with the rationale being, "God can resurrect a bowl of ashes just as conveniently as he can resurrect a bowl of dust." The 1908 Catholic Encyclopedia was critical about these efforts, referring to them as a "sinister movement" and associating them with Freemasonry, although it said that "there is nothing directly opposed to any dogma of the Church in the practice of cremation." In 1963, Pope Paul VI lifted the ban on cremation, and in 1966 allowed Catholic priests to officiate at cremation ceremonies.
Australia also started to establish modern cremation movements and societies. Australians had their first purpose-built modern crematorium and chapel in the West Terrace Cemetery in the South Australian capital of Adelaide in 1901. This small building, resembling the buildings at Woking, remained largely unchanged from its 19th-century style and was in full operation until the late 1950s. The oldest operating crematorium in Australia is at Rookwood, in Sydney which opened in 1925.
While open outdoor pyres were used in the past and are often still used in many areas of the world today, notably India, most cremation in industrialized nations takes place within enclosed furnaces designed to maximize utilization of the thermal energy consumed while minimizing the emission of smoke and odors.
A human body usually contains a negative caloric value, meaning that energy is required to combust it. This is a result of the high water content; all water must be vaporized which requires a very large amount of thermal energy.
A 68 kg (150 lbs) body which contains 65% water will require 100 MJ of thermal energy before any combustion will take place. 100 MJ is approximately equivalent to 3 m3 (105 ft3) of natural gas, or 3 liters of fuel oil (0.8 US gallons). Additional energy is necessary to make up for the heat capacity ("preheating") of the furnace, fuel burned for emissions control, and heat losses through the insulation and in the flue gases.
As a result, cremators are most often heated by burners fueled by natural gas. LPG (propane/butane) or fuel oil may be used where natural gas is not available. These burners can range in power from 150 kW (0.5 MMBTU/h) to over 800 kW (1.5 MMBTU/h).
Cremators heated by electricity also exist in India, where electric heating elements bring about cremation without the direct application of flame to the body.
Coal, coke, and wood were used in the past, heating the chambers from below (like a cooking pot). This resulted in an indirect heat and prevented mixing of ash from the fuel with ash from the body. The term retort when applied to cremation furnaces originally referred to this design.
Combustion system 
A typical unit contains a primary and secondary combustion chamber. These chambers are lined with a refractory ceramic brick designed to withstand the high temperatures.
The primary chamber contains the body – one at a time usually contained in some type of combustible casket or container. This chamber has at least one burner to provide the heat which vaporizes the water content of the body and aids in combustion of the organic portion. A large door exists to load the body container. Temperature in the primary chamber is typically between 760 to 1150 °C (1400 to 2100 °F). Higher temperatures speed cremation but consume more energy, generate more oxides of nitrogen, and accelerate spalling of the furnace's refractory lining.
The secondary chamber may be at the rear or above the primary chamber. A secondary burner(s) fires into this chamber, oxidizing any organic material which passes from the primary chamber. This acts as a method of pollution control to eliminate the emission of odors and smoke. The secondary chamber typically operates at a temperature greater than 900 °C (1650 °F).
Air pollution control and energy recovery 
The flue gases from the secondary chamber are usually vented to the atmosphere through a refractory-lined flue. They are at a very high temperature, and interest in recovering this thermal energy e.g. for space heating of the funeral chapel, or other facilities or for distribution into local district heating networks has arisen in recent years. Such heat recovery efforts have been viewed in both a positive and negative light by the public.
In addition, filtration systems (baghouses) are being applied to crematoria in many countries. Activated carbon adsorption is being considered for mercury abatement (as a result of dental amalgam). Much of this technology is borrowed from the waste incineration industry on a scaled-down basis. With the rise in the use of cremation in Western nations where amalgam has been used liberally in dental restorations, mercury has been a growing concern.
The application of computer control has allowed the cremator to be more automated, in that temperature and oxygen sensors within the unit along with pre-programmed algorithms based upon the weight of the deceased allow the unit to operate with less user intervention. Such computer systems may also streamline recordkeeping requirements for tracking, environmental, and maintenance purposes.
Additional aspects 
- Cremation time
The time to carry out a cremation can vary from 70 minutes to approximately 200 minutes. Cremators used to run on timers (some still do) and one would have to determine the weight of the body therefore calculating how long the body has to be cremated for and set the timers accordingly. Other types of cremators merely have a start and a stop function for the cremation, displayed on the user interface. The end of the cremation must be judged by the operator who in turn stops the cremation process.
See also 
- YouTube Crematory of Japan