CONSTEUCTION AJS^D FIRE PROTECTION OF COTTOX WAREHOUSES. 39 

 ROOF OPENINGS— VENTILATORS AND SKYLIGHTS. 



Openings in the roof such as are needed for ventilators and sky- 

 lights are permissible, though generally it is desirable that the sizes 

 should not exceed the minimum necessary. Ventilators should be of 

 metal, so designed as to be proof against the entrance of sparks from 

 tlie outside. A convenient size is the 12-inch or 18-inch diameter 

 round type of ventilator, of which there are a number of styles 

 on the market. The revolving cowl ventilators should be used for 

 the compress compartment. They discharge an enormous amount 

 of air, as they are not dependent on merely difference in temperature 

 ■within and without but are actuated also by a slight breeze. Either 

 type of ventilator may be combined with the skylight. Yentilation 

 may be given fey the arrangement of one or more sides of the sky- 

 light, as louvers, or with a slatted construction. In such case the 

 slats should be made of sheet metal rigidly set at an angle of 45° 

 ■or more with the horizontal and overlapping. Where ventilators of 

 any type do not provide satisfactory baffles to prevent the entrance 

 of sparks, the opening should have a screen of No. 16 wire woven 

 and galvanized, with a mesh of not over three-eigliths inch. 



The skylight in any case should be of metal frame, glazed with 

 one-quarter-inch wire glass — that is, glass having woven wire made 

 in it. Such glass will retard the passage of fire for a considerable 

 time, whereas the ordinary glass is soon shattered by the heat. 

 Moreover, wire glass is less easily broken out and so affords better 

 protection for the opening. The glass should be set securely in the 

 metal frame and made water-tight. 



Fire shutters for skylights and ventilators are not required, as 

 the chief hazard is assumed as from within. The resistance to fire 

 afforded by the arrangements described is sufficient to prevent a 

 rapid circulation of air and consequent rapid gTOAvth of fire, thus 

 affording the best opportunity for extinguishment by the automatic 

 sprinkler or hand appliances. Should these fail, however, the use 

 of hose streams will be facilitated by the opening of the skylight, 

 thus creating a draft and relie^dng the doors to some extent from 

 projecting flame. They also provide an opening for the injection of 

 hose streams.^ 



* Excellent skylight frames can be made of galvanized sheet iron of No. 24 

 United States gauge. Both the monitor and saw-tooth types of slcyliglit 

 are well adapted for the compress section, wliile the smaller metal frame 

 skylight is suitable for the storage compartment. Practical use generallj- 

 demands that the large glass sections of the saw-tooth or monitor skylight 

 of the compress comi>artment be arranged to open at times, though when 

 this is done the airangement should be such as to permit the opening, to be 

 protected by a wire screen as described for the ventilator. The skylight 



