How long and at what temperature does it take to cremated a body into ashes?

Back in 1980, fewer than 10% of Americans were cremated. This figure is now approximately 53%, according to the North American Cremation Association.

The change has been driven by various factors, ranging from religious and cultural beliefs to broader societal acceptance. However, no event has accelerated this shift more than the Great Recession (the global economic downturn of 2009). “We noticed the cremation rate increased as the economy declined in late 2008 and people lost their jobs. Cremation is a less expensive alternative to traditional burial,” remarked Jim Koslovski, Director of Rosehill and Rosedale Cemeteries in New Jersey.

Rosehill and Rosedale charge only $190 for cremating a body, adding fees for caskets, flowers, and other services. In contrast, a burial plot can cost $2,500, plus an additional $1,900 in fees.

How Crematoriums Work

Typically, when a hearse arrives at the crematorium, the deceased’s body is securely wrapped and placed in a casket. This practice reflects respect for the deceased and protects crematory technicians from infectious diseases, as well as ensuring the safe handling of remains before cremation.

The caskets enter the cold storage area of the crematorium. At Rosehill, they aim to conduct all cremations and return the ashes to the family within 24 hours. This aligns with the principle of timely burial in various states across the U.S.

Once preparations for cremation are ready, the casket is removed from cold storage and placed on a hydraulic lift that resembles a tray, then transferred to one of the cremation units (more commonly understood as a crematory, although Americans avoid using this term as it evokes thoughts of the crematoriums at Auschwitz during World War II).

A small error can have unforgiving consequences, so Rosehill employs two forms of ID to ensure families receive the correct remains. A copy of the receipt is attached outside the cremation unit, with a metal ID tag accompanying the deceased inside the unit.

A cremation unit has two chambers: the Main Chamber, where the body is placed, and the Secondary Chamber or “After Chamber”, which consumes the gases produced during the cremation process. The primary chamber typically has walls, floors, and ceilings lined with high-temperature concrete.

The main chamber (where the body is cremated) is heated to temperatures ranging from 760°C to 1,093°C for 1.5 to 2 hours.

The gases and particulates formed enter the after chamber, a 9-meter long maze designed to retain the gases for at least a second. The after chamber is built to withstand hot gas flows up to 927°C.

Cremation units at Rosehill. (Photo: CAREN CHESLER/Popular Mechanics).

“Any solid will turn into gas if heated to the right point. Essentially, that’s what happens to the body when the tissue is heated to the point where its solids turn into gases and become combustible. The key is to design the equipment to consume the majority of the emissions so that they comply with state environmental regulations,” stated Brian Gamage, Marketing Director of American Crematory Equipment in Florida.

According to environmental agencies in most U.S. states, the emitted particulates must be smaller than 0.1 on a standard 0.0283 cubic meter scale. Problems arise when the volume of gases (smoke) becomes too large for the after chamber to handle and spills over. This can happen if the machine is not properly designed or if the operator overloads the main chamber, which can occur for surprisingly trivial reasons – for example, placing an obese individual in the unit at the wrong time of day.

It may sound grim, but weight is a concern for crematory operators. The machine does not differentiate between a person weighing 150 pounds and one weighing 400 pounds; it simply performs its function.

The general rule of thumb for cremation is that 45 kg of human fat is equivalent to 65 liters of kerosene. If a person weighs 180 kg, at least 90 kg of that will be fat that burns quickly. If you place that person into a machine that is too hot, because cremation units tend to be hotter later in the day, the after chamber can emit smoke and odors profusely into the air.

While some crematories can handle bodies more quickly, a cremation unit can typically complete the process in about 1.5 hours. This time can vary depending on the weight of the deceased and the type of casket used. The time-consuming nature of the process limits the number of cremations each unit can handle per day.

Cremation process in images: (1) The body is identified, and the family permits cremation. Medical devices and prosthetics are removed, and jewelry is recovered before the body is placed in a combustible container. (2) The container is placed inside the cremation chamber and heated from 760°C to 1,093°C for 1.5 to 2 hours. (3) The remains are cooled, and the technician removes any metal fragments with a magnet. (4) The remains are ground into a fine powder. (5) The ashes are placed in a container, urn, and returned to the family. (Photo: CAREN CHESLER/Popular Mechanics).

After the cremation process is completed, the remains are placed in a silver baking tray. A technician runs a magnet over them to remove non-combustible materials from the cremation process. These items often come from pins, screws, hinges, and a person’s prosthetic joints. The technician then visually inspects and removes any materials the magnet missed, such as leftover glass fragments.

The crematory places the remaining bones and ashes into a pulverizer, which is unlike a food processor, to grind them into a more uniform powder. The ashes are then placed in a container for the family.

Returning to the Earth

Of course, cremation is not a new concept. Cremation dates back to the Stone Age and was common in ancient Greece and Rome. In certain religions, such as Hinduism, cremation, particularly outdoor cremation, is a very popular form of burial.

The rise of Christianity stifled cremation in the West. By 400 AD, around the time Emperor Constantine Christianized the Roman Empire, Rome banned cremation as a pagan practice. The theological reasons for this ban were related to resurrection – they wanted to keep the body intact so the deceased could be resurrected in the afterlife. Jewish law also prohibits it. By the 5th century, cremation had disappeared from Europe.

This practice saw a revival in Europe during the 1870s, primarily as an effort to curb the spread of disease.

The first modern crematory in the U.S. was built in 1876. By 1900, there were 20 crematories in the country. The practice gained further momentum in 1963 when the Catholic Church reversed its stance on cremation during the reforms of the Second Vatican Council, stating that cremation was permissible. Today, there are over 3,000 crematories across the U.S.

Jim Koslovski noted that the widespread acceptance of cremation aligns with practical conditions as cemeteries are running out of space. He estimates that Rosehill has only 15 years left before it runs out of room.

“Dust returns to dust” – Humans born from the Earth eventually return to the Earth. But how we return to Mother Earth is more than an emotional story – it is an environmental issue.

Urn for ashes. (Photo: GETTY IMAGES).

As cremation continues to be viewed as a leading alternative to burial, the emissions associated with this process have become a concern – to the extent that people are beginning to consider some alternatives to cremation.

There is now a water-based process called alkaline hydrolysis, invented as a way to dispose of animals infected with mad cow disease. It is marketed as a more environmentally friendly option for human disposal after slaughter, as it produces less carbon monoxide and pollution.

The alkaline hydrolysis process involves placing a body in a chamber filled with water and potassium hydroxide and heating it up to 149°C under high pressure. After three hours, the body becomes a brownish liquid, and the bones are soft enough to be crushed. The bones can be returned to the family, while the liquid can be disposed of in the sewage system.

Perhaps unsurprisingly, this method has not been particularly successful. It is slower than cremation. More importantly, this technology is more expensive: A stainless steel pressure vessel can cost anywhere from $175,000 for a basic unit to $500,000 for a high-end unit, while a cremation unit costs around $110,000. There are also legal issues because this process is prohibited unless a state passes a specific law allowing it.