28 BULLETIN 801, U. S. DEPARTMENT OF AGRICULTURE. 
RECENT AUTOMATIC DOOR CLOSERS. 
Closing devices much more sensitive than the fusible link are 
now available for use on fire doors. The fusible link requires heating 
of the solder and surrounding metal to a temperature above 165° F. 
The length of time required depends on the intensity of the heat 
at the door which may be placed some distance from the origin of 
the fire, or subject to conditions which would allow the fire to spread 
through the opening before closing action of the door. The improved 
closing devices either provide heat detectors at intervals over the 
ceiling or provide near the door a single heat detector which re- 
sponds to a sudden rise, of temperature. 
As an example of these principles, there is a device which is pro- 
vided with a heat detector which closes the door to which it is con- 
nected when the temperature rises more rapidly than is occasioned 
by weather or working changes. Iti is not necessary that the heat 
reach any fixed temperature, but simply that there be a sudden rise 
of temperature at the location of the heat detector which may be 
at the door or a distance from it, or there may be several detectors 
provided at different places. These detectors may be installed on 
both sides of the division wall and operate a door on either or both 
sides, the releasing mechanism usually being on the wall and near 
the door. The heat detector is connected with the door-releasing 
mechanism by an air tube and the motive power is supplied by the 
rate of rise in temperature at the location of any of the detectors. 
Such a device is extremely sensitive to heat, even though the source 
of the heat be in a distant part of the compartment. No con- 
nections of any kind independent of it are required and no elec- 
tricity is used. 
Another instance of a sensitive door closer is a device based, not as 
the first on relative change of temperature, but on response to a fixed 
temperature exceeding 165° F. with means of detecting such tem- 
perature placed in different parts of the compartment. This is 
accomplished by a device which makes an electrical connection when 
the given temperature is reached. With this system, electrical cur- 
rent may be taken from any constant supply or from a storage bat- 
tery or both. Unless the installation provides an alarm system 
which will indicate interruption in supply of current the battery 
should be used. This device also supplies an automatic fire alarm. 
It may be connected to the sprinkler system so that when this is called 
into play all fire doors will be closed. 
The new and improved door-closing devices are establishing a good 
record, but it must be remembered that the simple fusible link has 
given positive service and a reasonable degree of protection for many 
years. It is unwise to discard this simple link, but it is desirable 
that it be supplemented by one of the more sensitive devices if the 
