Section 7 Control instrumentation and alarms

7.1.1 An alarm system for monitoring the atmosphere in CA zones is to be installed which may be integral with the machinery space alarm system as required by Pt 6, Ch 1, 2.3 Alarm systems, general requirements.

7.1.2 Where alarms are displayed as group alarms in the main machinery space alarm system, provision is to be made to identify individual alarms at the refrigerated cargo control station.

7.1.3 The pressure in each CA zone is to be monitored and an alarm initiated when the pressure is too high or too low.

7.1.4 Where the RH notation is to be assigned, humidity sensors are to be installed in each of the CA zones and are to initiate an alarm when the relative humidity (RH) falls below or exceeds the predetermined set values.

7.1.5 Gas sensors or analysers are to be provided to monitor gas content in CA zones, see Pt 7, Ch 1, 7.3 Gas analysers and sampling and Pt 7, Ch 1, 7.4 Gas sensors.

7.1.6 Gas analysers and sensors are to be calibrated automatically once in every 24 hours. An alarm is to be initiated if accuracy is outside tolerance limits.

7.1.7 Direct readout of the gas quality within any CA zone is to be available to the operating staff on demand.

7.1.8 At least one automatic recorder is to be provided for the remote monitoring and recording of O₂ and CO₂ levels in each CA zone.

7.1.9 Alarms are to be initiated in the event of O₂ or CO₂ levels in each CA zone falling below or exceeding the predetermined set values.

7.2.1 Where air compressors are to be used for gas production, alarms are to be initiated for the following conditions:

• High lubricating oil temperature.
• High differential pressure across the filters.
• Electric supply failure.

The compressors are to shutdown automatically in the event of:

• High discharge air temperature.
• High discharge air pressure.
• Low lubricating oil pressure.
• High pressure in CA zone.

7.2.2 Instrumentation is to be fitted for indicating continuously:

1. Gas pressure.

2. Gas temperature.

3. Gas content.

4. Gas flow.

7.3.1 Where analysers are fitted, at least two analysers for oxygen and carbon dioxide having a tolerance of ±0,1 per cent by volume are to be provided to determine the content of the circulated gas within the CA zones.

7.3.2 Two separate sampling points are to be located in each CA zone and one sampling point in each of the adjacent spaces. The arrangements are to be such as to prevent water condensing and freezing in the sampling lines under normal operating conditions. Filters are to be provided at the inlet to sampling point lines.

7.3.3 Arrangements of the gas sampling points are to be such as to facilitate representative sampling of the gas in the space.

7.3.4 Where gas is extracted from the CA zones via a sampling tube to analysers outside the space, the sample gas is to be discharged safely to the open deck.

7.3.5 Provision is to be made for gas sampling by means of portable equipment as required by Pt 7, Ch 1, 9.6 Safety, alarms and instrumentation 9.6.3.

7.3.6 The sampling frequency is to be at least once per hour.

7.4.1 Where sensors are fitted, at least two sensors for each of O₂ and CO₂, having a tolerance of ±0,1 per cent are to be installed in each CA zone to monitor gas levels.

7.4.2 Gas sensors may be used for indication and alarm.