Taking damage from unseen source and catching fire at bedrock level

I use a Samsung Galaxy tab S2 8" inch tablet. I have been receiving damage and catching on fire while trying to clear a slime spawn block for slimes to spawn in. I am in seed -219636102. There is a 32 square block slime spawn zone at (480, 736) to (512, 768). The z and x might be flipped due to different orientations between blocktopograph app and the minimap mod. Any ways, while standing on the upper layer of bedrock excavating a room to spawn slimes I keep taking damage from an unseen source and occationally catching fire.