It is a requirement to install dirt traps at the end of all gas suppression system pipes in accordance with the National Standard for clean agent gas systems.
The standard states:
"A dirt trap consisting of a tee with a capped nipple, at least 50 mm long, shall be installed at the end of each pipe run."
This is for all gas suppression systems.
The fact that this is not shown on any hydraulic pipe calculation does not exclude its requirement. The hydraulic design programme will reflect an elbow, but this is to be replaced with a T piece.
SANS 306-4 is 10 years old and does not specify dirt traps. It does make note that filters should be used on smaller nozzles, but as no supplier offers filters, dirt traps should be installed on CO2 systems as well.
The purpose of the dirt trap is to catch any dust or dirt that may have accumulated in the pipe and prevent it clogging the orifice in the nozzle.