FOCUS
Modelling applications
Figure 3: FDS predictions for the time averaged received radiative heat flux at 1.6m above the floor for the three cases.
the received heat flux for the ‘2 walls’ case compared to the other cases. It also clearly indicates that for the apartment arrangement and design fi re chosen, the hob (when adjacent to two walls) should be located approximately 2m from the corner of the wall to reduce the significance of the corner effect when compared to the ‘1 wall’ arrangement. If the open plan design includes a corner positioned hob, the increased reflection of radiative heat should be considered in the calculations, and any radiative losses amended accordingly. With the above results obtained from the FDS modelling, the ‘Fractional Effective Dose’ (FED) methodology outlined in the SFPE Handbook of Fire Protection Engineering8
can
be utilised. This methodology calculates the thermal
radiation exposure, in terms of the received heat fl ux q (kW/m2
) from the source of the fi re. From
this, the cumulative FED, ∑FED, can be derived from the summation of all the FEDs of thermal radiation received while a person is making their escape. The point at which the FED limit is exceeded by the person making their escape
is when the escape route is deemed to be unacceptable. In terms of an acceptable upper limit of
FED to thermal radiation, guidance can be taken from BS 85249
pain threshold of 75(kW/m2
which suggested a lower )4/3
)4/3 . Where a large
proportion of particularly vulnerable persons (eg elderly persons in a residential care home) may be present, the use of 56.25(kW/m2
may
be more appropriate. The FDS modelling data can then be used
to inform a numerical calculation spreadsheet. This allows for the calculation of the thermal radiation received within a specific design arrangement while an occupant makes their escape, in addition to the cumulative FED, based on the location of the hob from the escape route. Figure 4 illustrates an example of the
spreadsheet interface, which calculates the heat fl ux, thermal does and FED received, taking into account the hob location with respect to all the factors discussed previously, ie travel speed, distance and time. The location of the most intense heat fl ux levels received can be easily
Figure 4: Example snapshot of numerical analysis interface.
26 DECEMBER 2018/JANUARY 2019
www.frmjournal.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60