A Study on Operating Positive Pressure Ventilator in Room Fires

Description

Positive pressure ventilators (PPVs) are increasingly used in building firefighting, referred to as ‘positive ventilation attack’. PPVs are intended to improve visibility and reduce air temperatures. However, firefighting with PPVs is only half as effective as fighting large, ventilation-controlled room fires in old buildings with small rooms used for mini-storage areas storing large amounts of combustibles. The addition of PPV air to such a fire causes a larger fire, faster heat release, and more toxic smoke. Therefore, operational guidance on PPV use is required to avoid converting ventilation-controlled fires into large fires. This guidance needs a scientific basis, especially for the effect of PPVs on room fires, which will be studied in the proposed project. Room fire dynamics will be studied in an example single room (4 m × 3 m × 2.8 m) under the action of a PPV. Firefighters reported difficulties judging whether the room with smoke coming out of a storage area was the fire room. To address this issue of complicated mini-storage geometry, the example room will be linked to another room (4 m × 9 m × 2.8 m) to study the action of PPV. This two-room model will be subjected to two sets of experiments at different scales (1:10 and 1:5). The PPV will supply air at various flow rates through an entrance door with various window-opening configurations in the example room. Fires with varying characteristics will be ignited under various ventilation conditions. The flame characteristics in the room model, such as colour, shape oscillations, and precision, will be investigated. Analytical studies on room fires were conducted under various ventilation conditions. The scale-model experiments will then be used to identify key hazardous scenarios for full-scale burning tests. The mathematical models of room fires will be developed to reproduce the observed burning behaviour in the room model under the action of PPVs. Numerical simulations using computational fluid dynamics will be applied to elucidate the fire-induced air flow. Scaling rules from the literature will be evaluated and modified to improve studying room fires with PPV. The proposed project’s findings will have a direct impact on rationalising and improving the deployment of PPVs during and after a fire.