with the rapid development of China's economy, the pace of people's life is accelerating day by day, and the traditional business model has undergone great changes. Especially in recent years, there have been two kinds of super-large business models, one is large-scale professional market, such as building materials market, furniture market, ceramics market, decoration market and so on. This kind of market is characterized by a single commodity but a large scale; The other is the form of commercial plaza, which is a commercial complex integrating shopping, entertainment, catering, film and television culture and other functions to meet people's one-stop consumption needs. The plane layout of this kind of building is usually complicated, with multiple functions intertwined and high personnel density. In case of fire, the pressure of evacuation is great. The above-mentioned two types of commercial buildings are often large in size and depth, which makes it difficult for the upper evacuation stairs to "go straight to the outside" on the first floor.

in view of the above situation, it brings two problems to the fire evacuation design: first, the daily use of large commercial buildings with different formats is different, so how to determine the number of evacuation personnel; Second, when a fire breaks out, by what means can people be quickly evacuated to the outdoor safety zone.

Determination of the number of evacuees in different formats

At present, large-scale businesses can be divided into two categories, one is large-scale professional markets, which are relatively single in variety and mostly in the form of commodity display, and a large number of goods are not in the market, so although the building area is large, the fire load is relatively small, and the density of people is also small. There is no separate breakdown of the number of personnel in this kind of business in the current Code for Fire Protection Design of Buildings (GB51116-2116), as shown in Tables 1 and 2. However, there are separate provisions in the local norms of some cities. For example, Code for Fire Protection Design of Large Commercial Buildings in Chongqing DBJ51-154-2116 is shown in Table 3. Another example is Shanghai's Technical Regulations on Fire Prevention for Large and Medium-sized Commerce (Hu Xiao Fa [2114] No.352), as shown in Table 4.

National Code

It can be seen from the above three codes that there is a big gap in determining the number of evacuees in large-scale businesses. The author thinks that the codes and regulations of Chongqing and Shanghai have obviously been carefully investigated, combined with the actual use of different commodity markets, further subdivided, and put forward different evacuation numbers, so they are more practical. This has a good reference value for architects to determine the number of evacuees when designing a large-scale professional market.

the other is the so-called "one-stop" shopping plaza, which has complex functions and dense people, and is very dangerous in case of fire. Its evacuation number should be calculated and determined in strict accordance with the current national fire code.

Several solutions for personnel evacuation

Due to the large volume of large commercial buildings and the large depth scale in both directions, it is difficult to ensure that each staircase can go straight to the outside when it reaches the first floor. In this regard, in the current architectural design, there are about the following solutions.

1. Evacuate directly to the outdoor

The distance from any point in the shopping mall to the evacuation stairs should be controlled within 31m, and if it is controlled within 37.5m with automatic sprinkler system, the evacuation stairs can be arranged along the external wall and directly to the outdoor according to the usual way. Sometimes when the evacuation staircase is not far from the external wall, it can also be used to expand the front room or set up a short safety walkway to make it go straight to the outside. However, this kind of evacuation is often difficult for a large number of commercial buildings.

2. Evacuation through the refuge aisle

In a large-scale building, due to the limitation of the upper evacuation distance, the evacuation stairs have to be placed inside the building, which leads to the failure of the first floor stairs to go straight outside. In this case, you can refer to the requirements of Article 5.2.5 in Code for Fire Protection Design of Civil Air Defense Engineering (GB51198-2119) to set up an evacuation walkway to evacuate people to the outside. However, due to the high requirements for the setting conditions of the evacuation walkway, it is required that the entrance to the evacuation walkway in each fire zone should be provided with a front room, and the front room should be pressurized and supplied with air. Moreover, the evacuation walkway will divide the first floor business premises into several blocks, which will bring a lot of inconvenience to the use, and at the same time, it will occupy the first floor area with the most commercial value. Therefore, in the usual design, architects use this method less.

3. Evacuate by means of "roofed pedestrian street"

A commercial roofed Kachiuchi street can be designed in the middle of a large number of commercial buildings. The width of the inner street should meet the corresponding fire-fighting spacing of buildings on both sides, and the length should not be greater than 311m. The inner street can be provided with a lighting roof, and the ceiling height should not be less than 6m. Smoke exhaust facilities shall be set at the upper part of the ceiling. If natural smoke exhaust is used, the opening rate of natural smoke exhaust should not be less than 25% of the inner street area. The stairs on the upper part of the building can be evacuated to Kachiuchi Street and then to the outside through Kachiuchi Street, thus solving the difficulty in setting the position of the upper stairs. But the distance from Kachiuchi Street to the outside should be no more than 61m. In fact, the design of this evacuation mode considers Kachiuchi Street as a sub-safe area.

Kachiuchi Street can be used as the main pedestrian passage of the whole commercial city for a large number of commercial buildings, which can fully reflect its commercial value and solve the evacuation problem at the same time. There are many examples of this evacuation method in practical application.

4. Setting of automatic opening roof

For large-scale and multifunctional commercial buildings, it is hoped that they can communicate in the same space when in use, but in case of fire, it is hoped that smoke can be exhausted quickly and people can be evacuated to the outdoor safety zone as soon as possible. In view of this demand, there is a product that can automatically open the roof in China. This product is a kind of glass roof set on the inclined track. At ordinary times, it is a daylighting roof. In case of fire, the glass roof can automatically slide down the inclined track to form a completely open roof. It can be electric or unpowered gravity automatic sliding down. When it is used daily, it is an atrium or a lighting inner street, which does not affect the daily commercial functions at all. When the roof is opened in case of fire, a complete outdoor space is formed. The outdoor space can also be used as a fire passage, through which firefighters can quickly enter the fire site and carry out targeted rescue operations. In this way, as long as the buildings on both sides meet the corresponding requirements of fire spacing, they can be regarded as two independent buildings, and the vertical fire shutter can be completely ignored. At the same time, in the spring and autumn season, you can also open the roof and use natural ventilation to improve indoor air quality. This method was first adopted in the third phase market of Yiwu International Trade City, Zhejiang Province, and the effect was very good, and it was also adopted in other large-scale commercial projects.

with the development of social economy, the scale and form of commercial buildings will certainly change; At the same time, with the rapid development of modern science and technology, the means of fire fighting will continue to innovate. In the future, architects will have more choices when designing fire evacuation for large commercial buildings.

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