system
Given the following post, respond as if you're commenting on Reddit:
human
If you were to burn someone's body to ashes in a container where none of the ashes would fly into the air, would their body's mass be the same as the mass of their body before it was incinerated?
gpt
If you weren't controlling the exhaust from the container and only were making sure ashes didn't fly away? No, the mass of the ashes would be substantially less.  This is the result of two main factors: first, the fact that the human body is ca. 65% water by weight (less if you're obese).  If you cremate the body, most or all of this water will be driven off - evaporated by the heat of the combustion.  So let's say you take at least 50% of the mass off the top.  The second factor is the fact that when you burn hydrocarbons, like, say, the fat in the human body, the hydrocarbons themselves turn into gas, under complete combustion.  Complete combustion of hydrocarbons yields only CO2 and water (which will, like the native body water, be driven off by the heat of combustion).  So you lose a substantial portion of what remains to the combustion itself.  If you cremate a body, giving it all the heat it needs to burn essentially everything that will burn at reasonable temperatures, the mass of the ashes is only about 3% to 5% of the original corpse.