valve is installed to bleed off pressure at 341 psi.
alarms to be actuated. Many of the operating
Another relief valve operates at 357 psi for rapid
devices discussed earlier in this chapter can be
release of excess pressure. There is also a frangible
used. Most commonly used are the heat-actuated
disk designed to burst at 600 psi should the relief
devices (H. A. D.) or smoke detecting devices.
valves fail to control pressure buildups.
Manual controlling devices are also used in
carbon dioxide systems. Whether the agent release
is automatic or manual, an alarm at the alarm
system control unit should be actuated.
There are advantages and disadvantages to
each type of carbon dioxide system. Low-pressure
storage units have a liquid level gauge that con-
Carbon dioxide fire protection system pipe
tinuously monitors the amount of carbon diox-
and fittings are selected to have suitable low
ide in storage. High-pressure systems require
weighing the cylinders. High-pressure systems
permit storage of almost the exact amount of
carbon dioxide required to protect a hazard area
because of the flexibility and selection of cylinders
in 50-, 75-, or 100-pound sizes. The smallest low
pressure is 750 pounds. High-pressure systems
require refilling and hydrostatic testing every 12
years. Low-pressure systems have no such require-
ment. Pressures in high-pressure systems vary with
the ambient temperature; this affects the discharge
rate of the system. Low-pressure systems keep the
liquid carbon dioxide at 0°F and 300 psi at all
times, assuring a uniform discharge rate. Another
advantage of low-pressure systems is their ability
to allow automatic, simultaneous discharge for
more than one hazard area on an engineered basis.
Hose reels can also be attached to these systems
to operate simultaneously with hazard protection.
temperature characteristics and good corrosion
resistance inside and out. Ferrous metals are
galvanized steel, copper, brass, and other
materials having similar mechanical and physical
properties are acceptable. Copper tubing with
suitable flared or brazed connections is also
acceptable. Cast-iron (gray) pipe and fittings are
Pipe and fittings for high-pressure systems
have a minimum bursting pressure of 5,000 psi.
In low-pressure systems, pipe and fittings have a
minimum bursting pressure of 1,800 psi.
Between the storage tank and selector valves,
black steel pipe may be used because of the larger
sizes involved and its airtightness.
The supply piping is usually routed to prevent
unnecessary exposure to high temperatures from
ovens or furnaces or to direct flame impingement
A reserve supply can be provided by increasing
the storage unit size of low-pressure systems.
High-pressure systems require manifolding and
valving arrangements to achieve a reserve supply.
Storage of the carbon dioxide is also a con-
sideration in showing advantages or disadvantages
of these systems. High-pressure systems require
approximately 3 pounds of equipment for every
pound. Usually, low-pressure systems require less
floor space for storage of equal amounts of
carbon dioxide as compared with high-pressure
systems. In many instances, low-pressure storage
containers may be placed outside of the buildings.
High-pressure systems allow flexibility in
space requirements since multiple cylinder banks
may be stored in several smaller locations.
Low-pressure systems require one large, single
area for the refrigerated storage unit.
As with all fire protection systems, carbon
dioxide systems must have operating devices for
discharge of the extinguishing agent and to cause
Figure 8-32.Carbon dioxide nozzles.