dew point and three degree rule

 

DEW POINT MEASUREMENT.

All decisions regarding cargo ventilation are based on the dewpoint temperature, comparing the dew point temperature ambient air with the dew point of the air inside the hold.

One of the simplest methods to find the dewpoint temperature is using a whirling psychrometer

By swinging the instrument inside the hold until the wet bulb temperature has stopped falling and remains steady.

All readings should be taken well away from air inlets ensuring that only hold air is tested.

●Enclosed space entry procedure should always be observed.

●Once the above information has obtained,

VENTILATE if the dewpoint of the air inside the hold is higher than the dewpoint of the air outside the hold.

DO NOT VENTILATE if the dewpoint of the air inside the hold is lower than the dew point of the air outside the hold.

THREE DEGREE RULE FOR DECIDING VENTILATION.

Sometimes, it is impossible to measure hold dew point accurately or at all. In such cases ventilation requirements may be estimated by comparing the avg cargo temperature at the time of loading with the outside air temperature several times a day and

VENTILATE if the dry bulb temperature of outside air is at least 3°C cooler than the average cargo temperature at the time of loading.

DO NOT VENTILATE if the dry bulb temperature of the outside air is less than 3°C cooler than the average cargo temperature at the time of loading.