Storage batteries subject to the provisions of this standard must be securely attached to the commercial coach. They must be installed in an area which is vapor-tight to the interior and ventilated directly to the exterior of the coach. When batteries are installed in a compartment, the compartment must be ventilated with openings of not less than two square inches at the top and two square inches at the bottom. Batteries must not be installed in a compartment containing spark or flame producing equipment, except in an engine generator compartment if the only charging source is the generator itself.