Large shop basement turned into a gym. Some concerns

A shop/filling station has a large basement which has recently been fitted out as a gym. I believe the owner of the gym is a family member of the filling station owner.
Built around 15 years ago.

There was an open day to which I went along and although it's a nice gym with new equipment etc, a few things concerned me and as I have no knowledge of construction or regulation, I thought I would ask here.

1. The ONLY access to this basement is through a concrete stairwell at the side of the building, through a single door which has a key operated lock from both inside and outside.
Could potentially get locked in with no means of opening from the inside.
There are no fire extinguishers in the basement.
In such a basement, what are the regs in terms of fire, escape and the door?

2. There is no ventilation apart from the door/stairway. The basement is completely below ground with concrete walls and ceiling.
Should there be a means of ventilation?
I would say with a few dozen people working out the air would change quite quickly.

3. In the corner, there appears to be a refrigeration unit for the shop above. It is boxed off with timber but the floor around it is wet with condensation. Should there be a gas detector here for any refrigerant used in case of a leak into the space ?

It looks like it will be a popular place but these concerns have given me second thoughts.