I figured it out with the help of Jugginator. If you have the multiplayer option for player killing set to no killing then you take zero damage from these. I forgot that I set that option to no killing when I play with my girlfriend and my sons so they won't shoot each other or me by accident. Have been doing this for years so when I play with them so I had no idea that it was saving my life from timed charges. The reason I even knew that I couldn't get hurt with them was that I placed one on a safe one day and everyone was body-blocking me. I couldn't get away in time and it went off but I took no damage. For those few seconds before it went off though I was screamin for everyone to get the hell out of the way and it was hilarious because it was a small space so we were all stuck. Hope this helps lol.
Fun Fact: I did some testing with player killing on and the damage range is so small you can place one on the edge of a frame and stand on the other edge of the frame and take no damage. Has to be the very edge though.