3.2 Determining the rate of air change
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC/Circular.729 – Design Guidelines and Operational Recommendations for Ventilation Systems in Ro-Ro Cargo Spaces – (Adopted on 4 July 1996) - Part 1 - Design Guidelines and Operational Recommendations for Ventilation Systems in Ro-Ro Cargo Spaces - 3 Testing the Ventilation System - 3.2 Determining the rate of air change

3.2 Determining the rate of air change

 The rate of air change is governed by the flow of supply air admitted to the ro-ro cargo spaces through the supply air openings. The flow of air can be determined using a direct reading of anemometer or other instrument of equivalent reliability.

Since the velocity profile of the air entering the vehicle deck through supply air openings on ships is generally highly unstable and fluctuates widely, the air flow should be measured by someone experienced in such measurements. However, after some training, responsible members of the crew should also be able to make these measurements.

Even when the measurements are made by competent personnel, allowance should be made for deviations of at least 20% from the actual air flow, when readings are taken by means of anemometers.

A description of air flow measurement procedures is given in appendix 2. Note that a high air change rate does not guarantee low contaminant levels. Poor mixing within the deck could lead to high contaminant levels and potentially high exposures, even though the fans appear to be providing a large amount of air. Once the ventilation system has been fully characterized, spot checks of the system should be made during actual loading or off-loading operations to ensure that the system is operating as expected. Further guidance is provided in Operational Recommendations for Minimizing Air Pollution in Ro-Ro Cargo Spaces (Part 2).

Parent topic: 3 Testing the Ventilation System
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