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2000 Fire Door-Fan Manual updated 2002-05-28 Page 32 of 58
Mixing or No Mixing (Descending Interface) or Extended Discharge
Mixing means that as agent leaks out the incoming air is continually
mixed with the remaining agent in the room so that the
concentration is constant throughout. Mixing gives equal protection
to all levels in the enclosure. Sometimes the air-handlers must
remain running during the retention time to keep equipment cool.
Other times mixing must be used because protection is required at
high levels. Often mixing is unintentionally created by convection
currents caused by hot equipment of equipment cooling fans that
must remain on during the retention period.
The initial concentration must be made greater to allow for the drop
in concentration.
This icon is used throughout the program and on reports to show
that mixing will take place.
To determine if there is mixing, a smoke test must be performed
where small puffs of smoke are placed near the protected
equipment. If the smoke puffs immediately dissipate, there is
continual mixing. If in doubt, it is possible to pass both the mixing
and the no mixing cases.
No Mixing or Descending Interface means that as agent leaks out
the incoming air is NOT mixed with the remaining agent in the room
so that a layer of air forms on top of the agent. NO Mixing gives
protection only below the air-agent interface.
The greater the initial concentration, the faster the agent will be
lost.
This icon is used throughout the program and on reports to show
that NO mixing will take place.