Page 268 - Valve Selection Handbook

Rupture Discs 255

If vented equipment must be located within buildings, it should be
located close to exterior walls so that the vent ducts will be as short as
possible, preferably no more than 3m long. 1
In the case of dust explosions hazard class KST up to 250 bar x m/s,
flame propagation can be prevented altogether by combining the vent
panel with a tube-shaped flame trap or flame-quenching vent system as
shown in Figure 6-38. By this construction, gases entering the flame trap
with a temperature of up to 1500°C (2700°F) leave the flame trap with a
temperature of less than 100°C (210°F). This temperature drop reduces
the escaping gas volume by a factor of approximately 10, compared with
unrestrained venting. All solids are retained by an integrated ceramic fil-
ter mat within the tube.
This construction allows explosion venting to be carried out within
closed rooms. Passages past the flame trap need only to be shielded
against surprise effect.

NFPA68 (1988), Guide for Venting of Deflagrations (5-4.4, Effects of Vent Ducts)