Is it dangerious to bench press on chair?

I have a pair of dumbells. I use a chair and a stool. I put them near each other and I lie on them with my back on the chair. I used a pair of 23.75 kilograms so far and never had a problem with the chair. Tommorrow, I'll try a pair of 25 kilograms for bench press. Do you suppose 1.25 kilograms difference for each dumbell would make any difference for the chair? By the way My body weight is now 69 kilograms.
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My back is on the chair and My ass in on the stool.
Is it dangerious to bench press on chair?
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