This paper describes the investigation of a passive ventilation solution to manage hydrogen concentrationwithin an ullage space (0.9 to 3m deep) in a large ullage space above a liquid (liquid surface area of ~80m2) containing ahydrogen source. The aim of the ventilation is to maintain the H2 concentration within the ullage space below 25% of the Lower Explosive Limit (LEL).

The programme of tests involved examination of the ventilation performance in terms of sensitivity to:

Chimney position
Hydrogen release rate
Hydrogen release point
Ullage height
Chimney diameter
The tests carried out lasted many hours, and the hydrogen concentration was monitored at a number of points within the ullage space. Pairs of ventilation 'chimneys' withassociated instrumentation systems were used to controland monitor the hydrogen concentration within the ullage space.

The paper will describe the approach to the testing, the results obtained and their analysis.