Passive ventilation

Ignition prevention by an automatic disconnection of the battery in case of an accident, separation of fuel supply lines and electrical systems, and design of proper systems for both active and passive ventilation, such as openings to allow hydrogen to escape upward. 

Swain, M.R., and Swain, M.N., Passive Ventilation Systems for the Safe Use of Hydrogen, submitted for publication in International Journal of Hydrogen Energy, February 1996. 

The design of the magazine and assembly stores incorporates a passive ventilation system that ensures that the fuel rods within the magazines and assemblies are maintained indefinitely at a safe temperature upon loss of the engineered cooling airflow. 

Calculate passive ventilation rates (driven by wind effects) to see if it is adequate to disperse the incoming gas... 

Hartless (2004) has demonstrated that in most cases for methane to reach explosive levels within a passively ventilated void there would need to be a significant failure of the passive ventilation (for example if all the vents become blocked) or the entry rate of gas would have to increase by orders of magnitude. For simplicity he assumed that the probability of such an occurrence was 0.01. One approach that is less subjective is to estimate the failure rate using the probability density method described previously (Box 6.4, see colour section). An example is shown in Box 6.8. However, it is difficult to allow for human factors when estimating the probability of failure for elements of a protective system and an element of professional judgment will always be required. Studying examples and guidance from other industries can also assist in this respect (e.g. chemical and oil industries). 

Underfloor natural (passive) venting wherever possible (or car park). Where passive ventilation is not feasible or cost effective use active venting or positive pressurisation... 

Passive subfloor ventilation (venting layer can be a dear void or formed using gravel, geocomposites, polystyrene void formers, etc.T Very good performance 2.5 Ventilation performance in accordance with Annex A of the British Standard. If passive ventilation is poor this is generally unacceptable and some form of active system will be required... 

Passive ventilation performance can be estimated using simple calculations. The most commonly adopted approach is described and examples are given for open voids and air flow through a void former. 

All types of floor slab as above. Proprietary gas resistant membrane and passively ventilated or positively pressurised underfloor sub-space. 

Taking the capabilities of removing methane in soil materials into consideration, it is estimated that in order to ensure the oxidation of methane at flow rates in the range of 0.01-2.5 m h the size of the biofilter should be at least 1 m of filter bed volume (Straka et al. 1999, Stresse Stegmann 2003, Haubrichs Widmann, 2006). The height of the open biofilters with passive ventilation, used for CH ehmination, must be lower than 1 m (Boeckx Van Cleemput, 2000, Stein Hettiaratchi, 2001, Park et al. 2002). 

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