Designing of evacuation measures

 

Requirements for emergency exits and escape routes and timing evacuation through exits are regulated by SNIP 21-01-97 «Fire safety of buildings and works».

To ensure the safety of people at fires escape routes are provided in buildings on which people can reach a safe place. When calculating the evacuation of two steps should be considered:

– Evacuation of people and property from separate premises;

– Evacuation of the buildings as a whole.

An emergency exits have the particular importance. According to a constructive solution of the constructive elements of the outputs must be greater or equal to the degree of fire resistance than building. Outputs consider evacuation, if they are:

a) from the premises of the ground floor directly to the outside or to the exit through the corridor, staircase, entrance hall;

b) from the premises of any floor in the corridors leading to the stairwell that is connected directly to the outside or through the lobby;

c) Improvement of any floor in adjacent rooms on that floor, secured outputs listed under a) and b).

The number of emergency exits shall be at least two.

To ensure the safe evacuation of the premises and buildings of the estimated time of evacuation t_p should be less than the time required evacuation t_rec:

                                        t _р <t_rec.                                             (10.2)

On the building plan applied emergency exits and escape routes. Estimated time of evacuation is determined based on the length of the escape routes and foot traffic speed on all sections of the road from the farthest point of the room to the emergency exits. When calculating all the way of human movement is divided into sections of length l_i and width σ_i. The initial areas considered passageways between workplaces, further areas determined on the basis of a building plan. The path is defined in the stairwell long by flight of stairs. Estimated time t_p should be found as the amount of time as the foot traffic on certain sections of the way:

                                                                      (10.3)

Time flow of people traffic on the first section of the path

                                                                                    (10.4)

The flux density D in this section of the route is determined by the formula:

                                    .                                (10.5)

where N₁  –  the number of people in the first section (defined by the teacher); f – average person horizontal projection area, m² (f = 0,1 m²  adult in summer clothes; f – 0,125 m² adult in winter clothes; f – 0,07 m² for a teenager).

The value is determined by the speed V₁ (see app. 15) according to D₁.

The intensity of foot traffic in the first section, m/min (per person / min):

                                          q₁=D₁ V₁.                                     (10.6)

The value of the speed of the flow of people V_i movement on the road sections, the following after the first take on app. 15 depending on the flow rate q_i,

                                       ,                    (10.7)

where δ_i, δ_i-1  – width considered i -th and preceding it (i-1)-th track section respectively, m; q_i, q_i-1 –  flow rate value of the subject i -th and the previous (i-1)-th path section respectively, m/min.

If q_i <q_max, then time of the movement at the path site determined by the formula:

                                 t_i=l_i/V_i,                                     (10.8)

 

and the value of q_max should be taken equal to 16.5 m / min for horizontal tracks; 19.5 m/min  for the door; 16 m/min  ladder down; 11 m/min  ladder up.

If q_i>q_max in the i -th step of the way people delay occurs. The delay time is determined by the formula:

                                                             (10.9)

If it unable to fulfill the conditions of q_i <q_max it is necessary to increase width δ_i, of this section to comply with conditions, or take the value V_i speed D = 0,9(app. 15).

In the case of a merger at the beginning of the section i two or more human flows intensity is determined by the formula:

                                                                  (10.10)

After determining all t_i values t_p determined by the formula (10.3), and then check the condition (10.2). t _rec value is determined by the table. 10.3.

Subject to the conditions (10.2) safe evacuation of people will be provided, otherwise it is necessary to reconsider the location of emergency exits, directions and dimensions of escape routes.

At the end of this section you need to make a brief conclusion.