Talking about the cause of fire in high-rise in London and understanding the ten principles of NFPA101 escape

The occurrence of the London fire affected the safety and security of tens of thousands of high-rise building users. On the one hand, we are glad that the disaster took place in the old professional fire big country, the United Kingdom. On the other hand, we are also worried that this disaster will once again evoke our own hidden concerns. High-rise building fires are so difficult to save. How should high-level residents be good?

Cause of fire

The reason why the fire was out of control was that many people understated that it was an ordinary refrigerator fire. The question is, why a fire in the refrigerator can cause serious disasters. Many people may not know that this is the inevitable result of the refrigeration industry responding to the environmental crisis and replacing the halogen refrigerant freon with the so-called “clean” refrigerant, which is one of the consequences of the transformation of environmental risks into safety hazards. At that time, there were many people of insight who were concerned about the risk of detonation of flammable refrigerants. Today’s London fire was merely to make forward-looking fears. Last fall, my mid-term exam questions for students in the safety professional compulsory course "Fire Dynamics" were as follows:

August 21, 2016 afternoon, the refrigerant spill Fujian Nan'an Merrill Chiu Yeung a two-storey brick house, triggering the explosion, resulting in the death of brother and sister.

This accident seems simple, but it is very representative and may occur in any air conditioner or refrigerator. Because modern environmental protection refrigerants mostly contain R290 (propane) and R600a ( i-Butane , isobutane), although only 60 to 80 grams , the leakage may still form a flammable and explosive environment in the room, causing catastrophic as a result of.

Although the physical characteristics of these refrigerants are environmentally friendly, they have brought about the safety hazards for many families. Based on the above information, calculate the following ( 8 points x 5 = 40 points):

1. If the fuel is isobutane ( i-Butane , the main fuel for the lighter), calculate the heat of combustion for isobutane based on the heat of formation of isobutane (see the n-butane parameters in the table on the right); if no heat is generated , Estimation of the heat of combustion of isobutane based on oxygen equivalent heat (Required Calculation and Estimation)

2. Calculate the maximum flame temperature using the heat of combustion (hint: @ stoichiometric ratio);

3. If the refrigerator contains 70 grams of isobutane, what is the total amount of leakage in the room and the most violent explosion?

4. If 70 grams isobutane is completely converted to TNT , how many kg TNT equivalents ( 1kgTNT = 4.23MJ ) ?

5. If the inerting point for isobutane is ( RLU=17.37 , XLU=0.5 ), how many grams of nitrogen will be required to fully dilute the isobutane (to LFC=1/(1+RLU )) so that it can be safe? Vented?

So, how to eliminate this hidden danger?

The use of binary refrigerants, the use of flammable refrigerants (environmental characteristics, high cooling efficiency) and non-combustible refrigerants (good safety features, cooling efficiency is not so high) can be mixed to reduce the combustible range of the mixture to avoid flammable Gas leakage prevents the effect of gas explosion. However, the refrigeration industry does not seem to care about this leakage. The key is that there is no promotion and advocacy of the insurance industry. Therefore, the research in this area is very few. The theory that I developed for it is also unattended. This is the face of the disaster in society. Inert.

Spreading reason

The reason why the fire was not saved was because the speed at which the flames spread along the outer wall exceeded the expected level, so the response rate could not keep up, leading to a tragedy of total loss of control. Why does it spread so quickly? This is a chimney effect.

In general, liquid fuels are afraid of space because space can accumulate air, resulting in a mixture of oxygen and gas, posing a risk of explosion. Similarly, solid fuel is also scared of space, and space will accumulate energy, causing energy that could have been dissipated to accumulate, preheating fresh fuel, and accelerating the spread of fire. Here, there is a buoyancy field brought about by the temperature difference, which will accelerate the spread of the flame, commonly known as the chimney effect (UK called Chimney Effect , the United States called Stack Effect ). In the atmosphere, if there is a temperature difference, there will be buoyancy (common sense in junior high school physics, nonsense in high school physics, truth in college physics). The greater the temperature difference, the greater the buoyancy, and the more obvious the buoyancy effect on the flame. At the same time, the external surface of the flame suppression, resulting in the flame of the fuel surface lodging, enhance the effect of heat transfer, accelerate the spread of the flame process.

The most controversial part of the London fire was the newly added insulation material is very ugly, so it added a protective cover, because the two are not close, there is a certain space, to provide an opportunity for the appearance of the chimney effect . This is what everyone knows.

Cause of injury

This unexpectedly large number of deaths and injuries is not usually the case. The three major causes of casualties are: late nights, lack of alarm and escape routes. Here are explained as follows.

Some people have noticed that this is a major period of fasting, so many Muslims do not sleep, giving evacuation jobs an opportunity to escape. However, we should also see that it is this religious habit of fasting during the day and eating at sea in the evening that has caused the disaster in the middle of the night. Everyone now believes that the cause of the fire is the refrigerator, indicating that someone must have seen the scene of a fire at the scene. This shows that changes in the user's lifestyle have also contributed to this unusual disaster. In this regard, the most famous example in China is the Dukezong fire, and it is always outsiders who catch fire. This is a disaster caused by the conflict between culture (differences in security habits and local customs).

Secondly, on-site lack of alarm means of the entire building, many people are awakened by external noise, rather than the alarm means itself, this point is still under investigation, the relevant responsibilities are great.

Third, there is a problem with the design of this building. There is only one escape stair and it happens to be in a space with the elevator. So once the space is on fire, both means of escape are finished at the same time. This is the result of the fire engineer's initial attention.

Perhaps the building was safe from the original design, but the renovation process added flammable insulation materials, making the original escape capacity seem inadequate. There are only one escape route for amateurs, so there is not enough escape capacity. The key to looking at the door is the length of escape.

If all the units are not far from the stairs (theoretically, the stairs in the building are the safest places to escape to the stairs), they can be designed as a single escape route.

The problem is that the original design does not have much fuel load, so it does not require too long a distance to move; the modified building increases the fuel load, so the original escape distance is inadequate.

All these fire escape designs are based on an important assumption that the stairwell door is closed at all times, and maintaining the normally closed state of the stairwell door is the key to protecting the stairwell from fire. The heavy casualties caused by the fire, there is a great possibility that the door to the stairwell is not closed.

The requirements of the United States NFPA101 (Life Safety Regulations) for escape routes can be summarized in ten principles:

1. A sufficient number of well-designed smooth escape means with sufficient capacity and arrangements.

2. If an escape means is blocked by flame, heat or smoke, there is an alternative means of escape for use. In other words, the escape is redundant.

3. In the crowd load to provide protection for means of escape in time to escape (Required Egress Time, RET) from operations and export capacity of the decision, to prevent the harm of flame, heat and smoke.

4. For those types of buildings where overall escape is not a major consideration (eg, high-rise buildings, it is not possible to move all evacuations). Divide the area to provide refuge by appropriate building isolation.

5. Protect the vertical openings and limit the operation of the fire extinguishing equipment to a single floor (prevent the spread of fire heads along the cable passages and staircases).

6. In the event of a fire, a smoke detection or alarm system is provided to remind residents and notify the fire department.

7. Provide sufficient lighting, correctly mark escape means and indicate direction correctly.

8. Equipment or areas that are protected from unconventional hazards, which may cause fires that endanger the residents’ escape.

9. Initiate, organize and practice effective escape exercises. In high-density and high-risk building types, escape guidance materials (such as escape route maps) and sound alarm systems are provided to facilitate adaptive escape behavior.

10. The use of interior finishing materials to prevent the rapid spread of fire or the generation of large amounts of smoke, the production of fire and smoke may endanger the residents' escape process.

The above ten principles can be further reduced to five principles:

1. Two escape doors as far as possible

2. Set additional escape doors based on number of people and danger level

3. Escape exercises require regular practice;

4. The distance to the escape door is reasonable;

5. The escape door has clear signs, no blocking, and adequate lighting.

Obviously, the buildings in the London fire had a violation of each of them. Therefore, it was a mistake in understanding, the so-called "man-made disaster." Through these human errors, we can better understand the fire dynamics in high-rise building fires and the safety principles of crowd dynamics.

The information in this article comes from the Internet and was reorganized and edited by China Rescue Equipment Network.