4. Except when used for special industrial purposes, such as oxy- acetylene welding, factories, lighthouses, portable apparatus containing not more than four pounds of carbide, and other special conditions as approved by the Association, the acetylene plant, such as generators, storage-holders, purifiers, scrubbers, and for washers, shall be in a suitable and well-ventilated outhouse, in the open, or in a lean-to, having no direct communication with a dwelling-house. A blow-off pipe or safety outlet shall be arranged in such a manner as to carry off into the open air any overmake of gas and to open automatically if pressure be increased beyond 20 inches water column in the generating chamber or beyond 10 inches in the gasholder, or beyond the depth of any fluid seal on the apparatus. 5. Generators shall have sufficient storage capacity to make a serious blow-off impossible. 6. Generators and apparatus shall be made of sufficiently strong material and be of good workmanship, and shall not in any part be constructed of unalloyed copper. 7. It shall not be possible under any conditions, even by wrong manipulation of cocks, to seal the generating chamber hermetically. 8. It shall not be possible for the lime sludge to choke any of the gas- pipes in the apparatus, nor water-pipes if such be alternately used as safety-valves. 9. In the use of a generator, regard shall be had to the danger of stoppage of passage of the gas, and resulting increase of pressure, which may arise from the freezing of the water. Where freezing may be anticipated, steps shall be taken to prevent it. 10. The use of glass gauges shall be avoided as far as possible, and where absolutely necessary they shall be effectively protected against breakage. 11. The air space in the generator before charging shall be as small as possible, _i.e._, the gas in the generating chamber shall not contain more than 8 per cent. of air half a minute after commencement of generation. A sample of the contents, drawn from the holder any time after generation has commenced, shall not contain an explosive mixture, _i.e._, more than 18 per cent, of air. This shall not apply to the initial charges of the gasholder, when reasonable precautions are taken. 12. The apparatus shall produce no tarry or other heavy condensation products from the decomposition of the carbide. 13. The temperature of the gas, immediately on leaving the charge, shall not exceed 212° F. (100° C.) 14. No generator shall be sold without a card of instructions suitable for hanging up in some convenient place. Such instructions shall be of the most detailed nature, and shall not presuppose any expert knowledge whatever on the part of the operator. 15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING ALLOWED." 16. Every generator shall have marked clearly upon the outside a statement of the maximum number of half cubic foot burners and the charge of carbide for which it is designed.