Cross passage pressurisation with non-incident tunnel impulse devices: approximation methodology for system design

摘要

For twin tunnel networks with cross passages there is generally a desire to "pressurise" the cross passage with air from the non-incident tunnel. Typically, cross passage pressurisation criteria is specified as a minimum air flow through the open door or a maximum door force. Different strategies can be used to achieve this, but fundamentally any successful arrangement will depend on achieving an appropriate pressure difference, at the location of the door, between the incident and non-incident tunnel. This paper investigates the use of impulse devices in the non-incident tunnel located at one end of the tunnel (corresponding to upstream of the fire in the incident tunnel) to achieve required pressurisation criteria. It is proposed that a non-incident tunnel velocity exists that will sufficiently pressurise an open cross passage regardless of its location, for a given fire scenario. However for some scenarios this may not provide the best outcome when both minimum and maximum desired door pressures are considered. The paper presents a simplified methodology that will allow a designer to determine the required non-incident tunnel velocity (and therefore equipment capacity) to achieve a given pressurisation requirement. One dimensional analyses using SES have been used to validate the approximations and provide an indication of accuracy as well as the range of applicability the methodology offers. The methodology provides designers with the limiting bands for sizing non-incident tunnel ventilation systems sufficient to achieve cross passage pressurisation for the strategy considered.