Check a number of rooms to determine the limiting

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Check a number of rooms to determine the limiting case. 3.6 Exposure to radiation along egress routes3.6.1 GeneralWhen occupants located within an exitwayor on an externalescape routemust egress past a window opening or glazed panel, they must not be exposed to a radiation level which will cause pain while evacuating. Therefore, the time to onset of pain (tp) must be longer than the exposure time (texp). The limitations for the analysis are as follows:a) The analysis requires that all occupants must have evacuated past the window opening or glazed panel within 10 minutes after ignition unless fire resisting glazingtested to a recognised national or international Standard is used. b) The maximum allowable radiation level that an occupant can be exposed to is 10 kW/m2.c) The analysis described here is only applicable for a single window. Multiple windows require more detailed analysis on the time to pain calculations where the time-dependent cumulative effect of the radiation can be accounted for (such procedures can be found in the SFPE Engineering Guide – Predicting 1stand 2ndDegree Skin Burns from Thermal Radiation).d) Analysis is not appropriate where occupants are likely to be mobility-impaired. e) Radiation through uninsulated fire resisting glazingcan be reduced by 50% (see k=0.5 in equation 3.6 below). f) Analysis is not required where an alternative escape routeis available.g) Analysis is not required where insulated glazing with fireresistance of not less than -/30/30 is used.h) Analysis is not required for sprinklered buildingswith window wetting sprinklers located on the same side of the window as the fireand designed and installed for that specific purpose.i) Analysis is not required during the period prior to ASETfor the room of fire origin.Verification Method C/VM2
DEPARTMENT OF BUILDING AND HOUSING – 10 APRIL 2012 I 117 Commentary: Paragraph 3.6.13.6.1The basic premise of this analysis is to demonstrate that an occupant egressing past a window opening is able to travel past the window without feeling pain from the thermal energy being emitted from the window. The analysis makes use of equation 3.7 to determine the time taken to experience pain when exposed to a given heat flux. The radiation is calculated using equation 3.6 to determine the maximum heat flux the occupant is exposed to when they are directly opposite the window and the distance where the emitting radiation from the window has dropped below 2.5 kW/m2. Example:In this example, we find the minimum safe separation distance from a window 2.0 m wide and 1.0 m high to an egressing occupant. The FLEDis assumed to be <400 MJ/m2so the emitting radiation level is taken as 83 kW/m2. (This example is intended to show the process and not to teach radiation heat transfer.) The analysis requires the engineer to carry out a number of view factor calculations, making use of the additive nature of view factors. The problem is solved either by trial and error or by using a ‘Goal Seeking’ algorithm in a spreadsheet.

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