Kapitel 115: Notary Enforcement.

There were two choices for him. He could try to use bombs to force the blast door open or go at it with his fist. But there was only one right choice for him, which was to go at it with his fists.

The blast door was designed to be resistant to explosives, so bombs won't do. Any bomb that could breach it is most likely to cause the whole floor to cave in. 

If he had the ability to hack electronics of the Psychic or Weapon class, he would have been able to open it easily. Unfortunately, he had only his fist for the job. 

He could also try to break down the wall, but that would be slower. He had found that the denser and stronger something was, the more effective explosive force was on it.

So a thick metallic door would be easier to bring down than a wall of cement, stones, and rebar. Besides, the wall is supposed to be two meters thick. A door that is 30 centimeters thick is simply better.