9. OUTSIDE GENERATOR HOUSES.--(_a_) Outside generator houses should not be located within 5 feet of any opening into, nor shall they open toward any adjacent building, and must be kept under lock and key. (_b_) The dimensions must be no greater than the apparatus requires to allow convenient room for recharging and inspection of parts. The floor must be at least 12 inches above grade and the entire structure thoroughly weather-proof. (_c_) Generator houses must be thoroughly ventilated, and any artificial heating necessary to prevent freezing shall be done by steam or hot-water systems. (_d_) Generator houses must not be used for the storage of calcium carbide except in accordance with the rules relating to that subject (_vide_ Chapter II.). _Class B.--Stationary Non-Automatic Apparatus_. 10. FOUNDATIONS.--(_a_) Must be of brick, stone or concrete. (_b_) Must be so arranged that the machine will be level and so that strain will not be brought upon the connexions. 11. GAS-HOUSES.--(_a_) Must be constructed entirely of non- combustible material and must not be lighted by any system of illumination involving open flames. (_b_) Must be heated, where artificial heating is necessary to prevent freezing, by steam or hot-water systems, the heater to be located in a separate building, and no open flames to be permitted within generator enclosures. (_c_) Must be kept closed and locked excepting during daylight hours. (_d_) Must be provided with a permanent and effective system of ventilation which will be operative at all times, regardless of the periods of operation of the plant. 12. ESCAPE-PIPES.--Each generator must be provided with a vent-pipe of ample size, substantially installed, without traps. It must be carried to a suitable point outside the building and terminate in an approved hood located at least 12 feet above ground and remote from windows. The hood must be constructed in such a manner that it cannot be obstructed by rain, snow, ice, insects or birds. 13. CARE AND MAINTENANCE.--All charging and cleaning of apparatus, generation of gas and execution of repairs must be done during daylight hours only, and generators must not be manipulated or in any way tampered with in the presence of artificial light. This will require gasholders of a capacity sufficient to supply all lights installed for the maximum lighting period, without the necessity of generation of gas at night or by artificial light. In the operation of generators of the carbide-feed type it is important that only a limited amount of carbide be fed into a given body of water. An allowance of at least one gallon of generating water per pound of carbide must be made in every case, and when this limit has been reached the generator should be drained and flushed, and clean water introduced. These precautions are necessary to avoid over-heating during generation and accumulation of hard deposits of residuum in the generating chamber.