Hi MantaRay, I’m happy to answer your question regarding the decomposition of human remains that are interred in crypts. Crypts have air vents and drains in them. The crypt floor has a slight slope to it to allow body fluids to flow towards the back of the crypt where the drain is, should they leak out of the casket. Using an unsealed casket allows dry air to flow over the remains. As the body decomposes, body fluids start to leak out of the remains. By having airflow, this allows the fluids to evaporate and allows for dessication of the body (drying up) The end result is a dehydrated, body. Some faces are recognizable and some are not. Each is uniquely different. There are many variables on how long this process could take. Are the remains inside an air conditioned mausoleum, or are the remains outside in wall crypts where the temperatures can get very hot. But it’s been my experience that the remains in a non-sealed casket are usually completely dessicated within 7-10 years. Sealer caskets on the other hand, do not allow any air to reach the remains or for any body fluids to evaporate. And that allows for up to several gallons of body fluids and embalming fluids for the remains to float in, and turn to mush. Eventually, the fluids will eat through the casket from the inside, and leak out into the crypt chamber. In some cases, it can run down the front of the crypt into the public area and make a horrific mess. Not only in sight, but smell as well. And don’t forget, that since a sealer casket doesn’t allow gasses to escape, the casket remains under pressure, and when it leaks, it comes out under force. Most crypts are designed and built to take care of this problem behind the scenes, so the public never knows. But in some cases, there are leaks. I hope this answers your question. I apologize for being graphic in my description, but I want to give you an honest answer. My credentials are over 35-years in the funeral industry.