The Cremation Process
Cremating a Human Body: Getting Down to the Nitty Gritty
The term "ashes" is a bit misleading, since what families receive after a cremation isn't a soft powder, but instead a grayish, coarse material, like fine gravel, made from the ground-up remains of bones.
In modern crematories, the body is stored in a cool, temperature-controlled room until it's approved for cremation. A coroner or medical examiner is often required to sign off to make sure no medical investigations or examinations need to be done since, unlike after a burial, the body can't be exhumed once it's cremated. The body is prepared by removing pacemakers, which can explode in the heat, prostheses and silicone implants. Radioactive "cancer seeds" -- injectable or implantable radioactive isotopes used to treat several types of cancer -- are also on the removal list. The body is then put into a container or casket made out of flammable materials such as plywood, pine or cardboard. In some countries, workers remove other external items such as jewelry or glasses, while other countries prohibit workers from doing so.
When the incinerator is preheated to about 1,100 degrees Fahrenheit (593 degrees Celsius), the mechanized doors are opened and the container slips quickly from a rack of rolling metal pins into the primary cremating chamber, also referred to as a retort.
Sometimes family members can watch the cremation from a window, or, in cases such as Hindu cremations, a family member can "start" the fire by pressing a button.
Once the door is sealed, the body is subjected to a jet-enginelike column of flame, aimed at the torso. The heat ignites the container and dries the body, which is composed of 75 percent water. As the soft tissues begin to tighten, burn and vaporize from the heat, the skin becomes waxy, discolors, blisters and splits. The muscle begins to char, flexing and extending limbs as it tightens. The bones, which are the last to go, become calcified as they are exposed to the heat and begin to flake or crumble.
An average human body takes from two to three hours to burn completely and will produce an average of 3 to 9 pounds (1.4 to 4.1 kilograms) of ash. The amount of ash depends usually on the bone structure of the person and not so much their weight. A newborn, which has mostly cartilage and very little set bone, might not even leave any remains after cremation.
Myth of the Exploding Skull
A common misconception is that the head of a burned body will explode if there is no wound or hole in it, much like a microwaved potato with no puncture in the skin. But forensics researcher Elayne Pope quickly deflated this urban legend when she conducted tests on 40 human cadavers. The myth probably arose when firefighters found the fragmented skulls of burn victims, not realizing that the skulls, which have a thin covering of tissue and quickly become brittle from heat, were easily broken by falling debris or water from their hose.
The cremation chamber, which is just big enough to accommodate one body at a time, looks a bit like the inside of a pizza oven and can reach temperatures of 2,000 degrees Fahrenheit (1093 degrees Celsius). It's lined with a heavy duty, high density fiber brick designed to retain heat. Those bricks eventually wear out with repeated expansion and contraction and are replaced once they are worn down to about half their original thickness.
Industrial cremators can run anywhere from $80,000 for a basic, entry-level model to $250,000 for the latest models. The modern-day incinerators are usually automated or computerized and can be programmed to adjust the temperature as needed. They burn natural gas, propane or diesel instead of the coke and coal that fueled retorts as late as the 1960s, allowing for more efficient and hotter burning while leaving little odor or smoke.
During the burning process, a second column of flame is fired up in a secondary chamber to burn off any particles or dust in the air leaving the retort, in order to reduce emissions, smoke and odors. Some retorts also have a wet scrubber in the emissions stack that sprays a mist of water so that escaping particles become trapped.
Once the body is completely burned, the chamber is then cooled and the cremated remains, which are often still recognizable as human skeletal remains, are swept with a long-handled hoe or wire-bristle broom into a tray. A powerful hand-held magnet is run through the ash to pick up metal parts left behind, such as fillings, plates and hip replacements, which can interfere with the grinding process. The metal parts are disposed with other biological material or recycled. The bones and remnants are put into a grinder, or cremulator, that uses ball bearings or rotating blades, like a blender. The remains are pulverized and poured into a plastic, lined container or an urn of the family's choice.
If the family requests, the ashes can be mailed via United States Postal Service, which requires a sift-proof box and signed confirmation upon receipt. UPS and FedEx don't ship ashes.
While there may be some inevitable residue mixing, the bodies are burned one at a time to ensure the separation of the cremated remains. Often, a disk identifying the person will be included with the remains throughout the process. Identification papers that travel with the body are placed on the outside of the incinerator and the box of ashes is also tagged and identified to avoid a mix-up.
Some photos of cremation.