Fire Safety to be connected to emergency back-up power supplies, similar to sprinkler and standpipe systems, so that in the event of a power outage the moisture content of the plant material would not drop below the threshold for ignition. Moisture content was also shown to reduce more rapidly when the vegetation was exposed to higher radiant heat fluxes, meaning the location of greenery systems relative to high fuel load areas within the building should be carefully considered, i.e. a system located on the façade of a retail building would likely be more limited in the number of plant species it could contain when compared to a system on an office building, as retail fires will produce significantly higher radiant heat fluxes than office fires. Specific studies on fire spread following ignition of vertical systems are scarce, largely due to a limited number of actual fires occurring in these systems, as well as the wide range of plant species that they can contain. This means that each system needs to be assessed deterministically on a case-by-case basis. That would be done using traditional fire engineering analyses related to flame height and impingement, fuel consumption, burn duration and radiant heat flux exposure, in order to evaluate the expected rate of flame spread and inform the geometrical design of the system accordingly. CFD analysis can then be carried out to assess potential wind effects, considering the fuel and moisture content, topography, relative humidity, and ambient air temperature.
Figure 5 - Flashover propensity of common plant species used in VGS [4]
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Following these assessments, the system will either be considered to satisfy the code intent, thereby functionally complying with code requirements, or would constitute a reduction in the standard of safety below that prescribed by the code. In such case, additional mitigation measures would be required including passive and active fire protection systems, additional firefighting facilities, or enhancements to means of egress provisions. For this reason, for vertical systems to be possible without significant redesign of the fire strategy, they need to be proposed at the early design stages before many of the key fire safety components are fixed.
