2.1 SymbolsTo illustrate the procedure,
the following notation is used: t
stair = stairway
travel time(s) of the escape route to the assembly station
t
deck = travel time(s) to move from the farthest
point of the escape route of a deck to the stairway
t
assembly = travel time(s) to move from the end
of the stairway to the entrance of the assigned assembly station
2.2 Quantification of
flow timeThe basic steps of the
calculation are the following:
.1 Schematisation of
the escape routes as a hydraulic network, where the pipes are
the corridors and stairways, the valves are the doors and
restrictions in general, and the tanks are the public spaces.
.2 Calculation of
the density D in the main escape routes of each deck. In the
case of cabin rows facing a corridor, it is assumed that the
people in the cabins simultaneously move into the corridor; the
corridor density is therefore the number of cabin occupants per
corridor unit area calculated considering the clear width. For
public spaces, it is assumed that all persons simultaneously
begin the evacuation at the exit door (the specific flow to be
used in the calculations is the door.s maximum specific flow);
the number of evacuees using each door may be assumed
proportional to the door clear width.
.3 Calculation of the initial specific
flows F
s, by linear interpolation from table 1.1, as
a function of the densities.
.4 Calculation of the flow F
c for
corridors and doors, in the direction of the correspondent
assigned escape stairway.
.5 Once a transition point is reached, formula
(1.7) is used to obtain the outlet calculated flow(s)
F
c. In cases where two or more routes leave the
transition point, it is assumed that the flow F
c of
each route is proportional to its clear width. The outlet
specific flow(s), F
s, is obtained as the outlet
calculated flow(s) divided by the clear width(s); two
possibilities exist:
.1
F
s does not exceed the maximum value of table
1.2; the corresponding outlet speed (S) is then taken by linear
interpolation from table 1.3, as a function of the specific
flow; or
.2 Fs
exceeds the maximum value of table 1.2 above; in this case, a
queue will form at the transition point, Fs is the maximum of
table 1.2 and the corresponding outlet speed (S) is taken from
table 1.3.
.6 The above procedure is
repeated for each deck, resulting in a set of values of
calculated flows F
c and speed S, each entering the
assigned escape stairway.
.7 Calculation, from N (number of persons entering
a flight or corridor) and from the relevant F
c, of
the flow time t
F of each stairway and corridor. The
flow time t
F of each escape route is the longest
among those corresponding to each portion of the escape route.
.8 Calculation of
the travel time tdeck from the farthest point of each escape
route to the stairway, is defined as the ratio of length/speed.
For the various portions of the escape route, the travel times
should be summed up if the portions are used in series,
otherwise the largest among them should be adopted. This
calculation should be performed for each deck; as the people are
assumed to move in parallel on each deck to the assigned
stairway, the dominant value tdeck should be taken as the
largest among them. No t
deck is calculated for public
spaces.
.9
Calculation, for each stair flight, of its travel time as the
ratio of inclined stair flight length and speed. For each deck,
the total stair travel time, t
stair, is the sum of
the travel times of all stairs flights connecting the deck with
the assembly station.
.10 Calculation of the travel time tassembly from
the end of the stairway (at the assembly station deck) to the
entrance of the assembly station.
.11 The overall time to travel along an
escape route to the assigned assembly station is: t
I
= t
F + t
deck + t
stair +
t
assembly (2.2.11)
.12 The procedure should be repeated
for both the day and night cases. This will result in two values
(one for each case) of tI for each main escape route leading to
the assigned assembly station.
.13 Congestion points are identified as
follows:
.1 in those spaces where the initial
density is equal, or greater than, 3.5 persons/m
2;
and
.2 in those
locations where the difference between inlet and outlet
calculated flows (F
C) is in more than 1.5 persons per
second.
.14 Once the calculation is
performed for all the escape routes, the highest t
I
should be selected for calculating the travel time T using
formula (1.8).