Chamber top assembly pressure relief requirements vary according to the application.
Requirements for the levels of ventilation defined in BS EN 124 (minimum 5%/140cm2 of the frame clear opening) are unusual.
Customers often require the covers to ensure gas pressure cannot accumulate within the associated chamber.
In pressure relief applications such as this, where full ventilation defined by BS EN 124 is not required, Wrekin adds a series of 20-25mm dia. apertures to increase the open area of a manhole top provided by the products' existing features.
Note: Where pressure relief is offered for a particular product, Wrekin has notified BSi of the intended modification and verified that the modification will not compromise the ability of cover structures to withstand the loads required by the respective BS EN 124 category.
Where a large pressure relief area is required (e.g., in line with the BS EN 124 requirement), we recommend considering an unmodified gully grating product rather than structurally compromising a chamber top assembly with excessive pressure relief apertures.
