CONSTRUCTION AND FIRE PROTECTION OF COTTON 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 
the 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. Ventilation 
may be given by 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 c 
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 Xo. 16* wire woven 
and galvanized, with a mesh of not over three-eighths inch. 
The skylight in any case should be of metal frame, glazed with 
one-quarter-ineh 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 growth 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 relieving the doors to some extent from 
projecting flame. They also provide an opening for the injection of 
hose streams. 1 
1 Excellent skylight frames can be made of galvanized sheet iron of No. 24 
United States gauge. BotH the monitor and saw-tooth types of skylight 
are well adapted for the compress section, while the smaller metal frame 
skylight is suitable for the storage compartment. Practical use generally 
demands that the large glass sections of the saw-tooth or monitor skylight 
of the compress compartment be arranged to open at times, though when 
this is done the arrangement should be such as to permit the opening to be 
protected by a wire screen as described for the ventilator. The skylight 
