Alarm Strategies; Emergency Purge Feature; Emergency Purge Operation - Siemens 125-5033 Owner's Manual

Fume Hood Controller Owner's Manual

Alarm Strategies

One approach is to use the ALARMs to indicate a condition that requires immediate attention
and the WARNINGs to indicate a condition that may require attention but is not urgent. In that
case, the alarm limits would be set to indicate that it is unsafe to work at the fume hood. The
warning limits would be set at a level that is safe, but indicates that the system may not be
operating correctly. These values should be selected by the person responsible for laboratory
safety.
The delay timer is adjustable and should be selected with safety in mind. Laboratory safety
procedures will not be effective if there are numerous nuisance alarms. The delay timer
should be set at a sufficiently large interval to prevent nuisance alarms. However, if the delay
timer interval is excessively large, there is a risk of having a laboratory worker standing in
front of an ineffective fume hood for a prolonged period. The delay timer interval should be
selected by the laboratory safety officer with the above considerations in mind.

Emergency Purge Feature

Under certain emergency conditions, such as a spill in the fume hood, it may be necessary to
purge the air from the fume hood. The Emergency Purge sequence enables the fume hood
user to override normal airflow setpoint and temporarily increase the airflow beyond the value
needed to maintain the airflow setpoint.
The Emergency Purge overrides any other control mode in the Fume Hood Controller and
has two modes of operation; maximum purge, and controlled purge.
The maximum purge moves the exhaust airflow control device to full open and holds it there
regardless of airflow. This mode has the advantage of providing immediate expulsion of the
contaminating agent, but may cause airflow problems in the fume hood and reduce the
airflow capacity at other fume hoods.
The controlled purge continues to modulate the exhaust airflow control device and controls
the airflow, but at a higher than normal level.
The Fume Hood Controller can be set up to purge in either mode or to start in maximum
purge and then switch to a controlled purge after an adjustable amount of time.

Emergency Purge Operation

The Emergency Purge sequence is initiated by pressing the Emergency Purge button on the
ODP. When the Emergency Purge button is pressed, the fume hood will go to the maximum
purge for the time selected in the emergency timer. After the emergency timer elapses, the
Fume Hood Controller will begin actively controlling the airflow, but at an increased setpoint.
The Emergency Purge sequence is canceled by pressing the Emergency Purge button a
second time. The ODP indicates an Emergency Purge sequence in three ways:
•
The red LED illuminates.
•
The horn sounds.
•
EMERGENCY PURGE and EEE display.
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