Per 
SCP-5458 taken at [REDACTED]
Special Containment Procedures:
SCP-5458 is to be contained in an 8m x 4m x 4m air-tight, steel cell. A ventilator and a tube connecting to a hydrogen chloride (HCL) tank are needed in the cell. Surveillance cameras and a thermometer are also to be installed. The enclosure must not have any sources that could change the cell's temperature except for SCP-5458 itself. The cell also must have an air-tight vestibule door.
Anyone who enters the cell must wear air-tight clothing and a gas mask; no skin can be exposed. The SCP-5458-1 neutralization procedures also need to take place every five days in order to prevent an SCP-5458-1 containment breach.
Description:
SCP-5458 is an anomalous Brunswick piano currently kept at Site-█. SCP-5458 must be constantly performed without any mistakes made when played. If any of this is violated, a transparent gas capable of corroding through human flesh will be released from the back of SCP-5458 within 20 seconds. The gas is classified as SCP-5458-1.
SCP-5458-1 can be produced infinitely by SCP-5458; it is currently impossible to find the cause of the production, and it is impossible to stop the production permanently.
According to the results of experiments tested on D-Class subjects by Doctor ██████, when exposing a human to SCP-5458-1 without any protective clothing, the subject will die within 2 - 5 minutes due to blood loss if not treated properly and 10 - 25 seconds if inhaled, making the gas very dangerous to humans. It is also tested that when SCP-5458-1 is released, it will significantly increase the surrounding environment's temperature. This can be used to detect SCP-5458-1's presence.
SCP-5458-1 cannot be destroyed but can be neutralized into SCP-5458-2 when reacted with hydrogen chloride. SCP-5458-2 is not corrosive, nor does it have any adverse effects on humans. SCP-5458-2 is usually ventilated out of the building after the SCP-5458-1 neutralization procedure is complete. Interestingly, SCP-5458-2 is weighed to be 1.29 times lighter than hydrogen gas, which is an anomaly thought to be scientifically impossible.
SCP-5458-1 Neutralization Procedures:
Bleach will first be applied onto SCP-5458 to protect the entity from any corrosion of the chemicals. 108L of hydrogen chloride will then be released into the cell. It will take approximately 5 minutes for the hydrogen chloride to neutralize all present SCP-5458-1. Extra hydrogen chloride is then to be released, and the cell is to be left for five additional minutes before ventilating all SCP-5458-2 and remaining hydrogen chloride out of the building. Fresh air will then be released back into the cell.
Discovery and Investigation:
SCP-5458 was first located in an abandoned house in ████ ██████, Israel. It was found in a basement with four human remains and an old man performing on the entity. SCP-5458 was seized during an MTF Beta-7 ("Maz Hatters") raid when three residents and a local policeman were reported missing after exploring the house. An MTF agent (B7-3) and the old man were both killed due to contact with SCP-5458-1.
After a thorough investigation of the house, traces of a cult named "Isaiah Lebar" were found. Ethnicity DNA tests from bloodstains also lead to an Israeli village called Quaal. MTF agents searched Quaal for the cult. However, no traces were found except a book titled «Testaments of Isaiah Lebar».
Addendum:
Below is a section of the transmission log between Doctor ██████ and three MTF Beta-7 team members (B7-1, B7-2, and B7-3). This was recorded when the anomaly was identified in the house and when B7-3 and the old man were killed.
Exploration Transmission Log Transcript
Date: ██/██/████
Exploration Team: MTF Beta-7 ("Haz Matters")
Subject: SCP-5458
Team Members: B7-1, B7-2, B7-3
Doctor ██████: B7 team, do you copy?
B7-1: Copy, sir.
B7-2: Copy.
B7-3: I copy.
B7-2: Oh, it’s starting to smell really bad down there.
B7-3: Gosh, it’s… bad.
Doctor ██████: Keep going, don’t stop.
Doctor ██████: Do you guys hear anything?
B7-1: Not really… Wait, no, I hear some sort of music.
B7-2: I think it is a piano.
Doctor ██████: That’s right, go in, go in the room quickly, put on your masks.
B7-1: We have it on, we are entering the room now.
B7-2: We are in, it appears that someone is playing on a piano…
B7-3: The room is stained with rotten blood, there are corpses everywhere what the hell!
Doctor ██████: You guys are on track, seize this "someone" and the piano
B7-2: Yes sir.
B7-1: Get onto the floor now!
B7-2: He seems to be an old man.
B7-2: Do not move, stay on the floor. You [INAUDIBLE] are gunna get your self killed.
B7-3: He’s being handcuffed.
B7-1: [INAUDIBLE].
B7-2: There are many corpses around here, from the texture, I think it has been rotting for a while…
Doctor ██████: Good job, you guys need backup?
B7-1: Room is clear, we need backup to carry the piano.B7-3: It’s getting very hard to breath.
Doctor ██████: Sending more agents in. You guys will have to wait for three minutes. Do you copy?
B7-2: Copy.
B7-1: I copy, sir.
B7-3: Aw fuck! It hurts! Shit. Ouch. I’m gunna start bleeding!
Doctor ██████: Evade the room. Dash three do you copy? What is happening?
B7-2: Call for medical backup, dash three is bleeding uncontrollably, we are unsure why.
Doctor ██████: Help is on the way, where exactly are you bleeding? Do you have your
ma-B7-3: NO DAMNIT I DON’T, FUCK, SHIT IT HURTS LIKE HELL! PLEASE… HELP ME.
B7-1: dash three didn’t have his mask on, I think it is [INAUDIBLE] some form of gas. We are evading him out of the room currently, shit, his head looks like a tomato. Blood is everywhere.
B7-3: [INAUDIBLE], I am gunna die!
Doctor ██████: Dash three, do you copy? Dash three?
B7-2: He’s unconscious, sir.
Doctor ██████: Evade the room immediately.
B7-1: Shit, I think he is dead.
B7-2: The old man is also bleeding, it is screaming sir.
Doctor ██████: Forget about the old man, do NOT take off your masks, get the hell out and close the damn door. Do you copy?
B7-2: Yes sir.
B7-1: Copy.
