Per 
Special Containment Procedures: SCP-5189 is kept in a cell made of titanium on the walls, floor, and ceiling of the containment and they all must be 2 layers thick or else it could escape. The door is a vault door and right on the other side is a decontamination chamber. All personnel that enter the containment must wear a hazmat suit with 2 5ft long oxygen tanks and have all possible ways for gas to get in (other than the oxygen) sealed. When leaving the containment, all personnel will be unsealed and decontaminated before leaving.
Description: SCP-5189 is an immense, thick, black smog that emits dangerous levels of radiation. Upon contact with SCP-5189, the subject who we'll call SCP-5189-S we deteriorate and burn at an alarming rate.
Discovery: In 1999, 2 MTF bodies were found almost completely burned to the bone with traces of gas being in their bodies. The foundation couldn't pinpoint the exact gas though. The next night, 6 MTF went back to see if there were any more indicators on where this gas came from but instead, they were met with death. The site director Dr. Gavins was more intrigued than freaked out so he sent more MTF back but with hazmat suits this time. They captured a sample within the hour. Dr. Gavins had never seen anything like it so he decided to it was SCP worthy. To see what it did upon contact with different objects, he placed it in a containment chamber and let it out its container. Here are the audio logs.
Audio Log#1:
Dr. Gavins: yesterday was the first SCP we found in 63 days, 4 hours. I'm quite intrigued by SCP-5189 and want to run more tests on it to see its full capabilities. Tomorrow, I'm going to have Dr. Fuller see what it does to an object because all I've seen it do is harm humans.
Audio Log#2:
Dr. Gavins: 2 days ago, we found out it can harm anything. We did a test on concrete, metal, wood, dead rats you name it but it seemed that rats last longer than humans. We had a Class D that wanted to participate in the experiment. So naturally, we said no because you are still alive and we need a dead test subject but she seemed to really want to. So we injected her with propofol and she was out like a light. We then injected her with poison and she died very quickly so we were ready. The batteries are low so I'll end this here.
Audio Log#3 the last one:
Dr. Gavins: So picking up where i left off yesterday, we put her deceased body in the cell and it lasted about 2 minutes and 14 seconds before the skin was burning and turning a weird blue-ish green color. The rats on the other hand lasted about 5 minutes and 8 seconds before being "withered" as I like to call it.
Addendum: SCP-5189 was originally classed as Euclid but rebranded as Keter.
Cause: multiple deaths at the site including Class D and scientists. For instance, one Class D, in particular, tried to escape 1 week after SCP-5189 was contained. This was bad for the Class D because he knew there was a vent that led right to the surface but, the then empty containment holding the vent now contained SCP-5189. The Class D got into the (containment. at this point, there was only a singular decontamination chamber) This Class D thought it was some sort of weapon so he took it and started to get into the vent and that's when he started no get a burning sensation everywhere on his body. He fell down and broke the glass jar that SCP-5189 was in. It started to consume him. The only way to describe this feeling is a burning pain that gets worse every second you are in the smog. You start to notice your fingers melt and blacken. Then, before you know it's over. Another instance, a scientist was found dead outside the cell he stayed late, and one of the scientists that went in there earlier didn't close he door all the way resulting in the other scientists' death.
