【Abstract】 what frightened every firefighter mostly is that he finds the air will be running out before his retreat. Though firefighters are trained rigorously and disciplined severely before assignment, it always possible that because of the complexity of fire scene, retreat later than the plan, evacuation route blocked, getting lost on the site, firefighters haven’t left the fire scene while the air in the respiration was used up. This paper is going to take a discussion on the emergency measures of dealing with respirator air exhaustion, and advance a proposal to equip firefighters with filter canisters which have express interface to mask. This research will provide useful protection when the firefighter is in the danger of exhaustion of the air in respirators.
【Keywords】respirator; exhaustion of the air; fire scene; emergency measure; emergency equipment
0 Preface
When a fire occurs, the combustion of combustible materials will produce a large amount of gas, heat and smoke, among which the smoke and gas are collectively called fire smoke, which is generally composed of a mixture of suspended solids, liquid particles and gases produced by combustion. The main components of flue gas are solid particles and toxic gases such as carbon monoxide, carbon dioxide, hydrogen sulfide, and hydrogen cyanide.
The smoke from the fire will spread the fire, affect the sight of people, cause high temperature burns and cause poisoning, and cause great harm to the human body. According to statistics, most of the deaths in the fire scene are caused by smoke inhalation. Therefore, for firefighters performing tasks on the fire scene, respirator is one of the most important equipment to protect personal safety.
1 Status of use of firefighters’ air breathing apparatus
1.1 Structural composition and working principle of air respirator
At present, in the process of fire fighting and rescue in our country, the main breathing apparatus equipped is positive pressure air breathing apparatus (referred to as air breathing apparatus). The composition of positive pressure air respirator is generally divided into: mask, air supply valve, gas cylinder, pressure reducer, back support respirator, the gas tank capacity is generally 6.8L, and the gas cylinder is an aluminum alloy liner carbon fiber wound composite gas cylinder” , It has the advantages of safety and stability, strong pressure resistance, light weight, comfortable wearing and stable performance. The high-pressure compressed air is stored in the bottle, and the working pressure is 30MPa. After the high-pressure air in the gas bottle is decompressed by the pressure reducer, it enters the medium pressure The airway is sent to the air supply valve, and the air supply valve is connected to the mask, and the medium pressure gas is decompressed to the pressure that the human body can breathe according to the user’s inhalation. The part of the mask for the user to breathe is used to cover the face and isolate toxic , Harmful gas enters the human respiratory system. There is an exhaust valve on the mask to discharge the gas exhaled by the user, and the inside of the mask maintains a positive pressure. The exhaust valve is a one-way valve, which can only exhale but not inhale to ensure the safety of the user. The back support is used to support the cylinder part and the pressure reducer part, and keep the whole set of positive pressure air respirator and the user well worn.
1.2 Use of air breathing apparatus
Before performing firefighting and rescue tasks, every firefighter needs to undergo strict respirator training, including adaptive training and breathing management training. Adaptive training is to let firefighters wear air respirator for daily subject training, so that firefighters are accustomed to using air respirator for breathing, accustomed to wearing air respirator to carry out offensive operations and safe evacuation, and through repeated training, find people and equipment. The best combination and make the body form a memory. Respiratory management training requires firefighters to avoid unnecessary physical exertion as much as possible to reduce oxygen consumption; respiratory management training also requires firefighters to keep calm in critical moments, maintain a lower limit of breathing, not blindly consume oxygen, and actively. Find the best way to deal with it.
The fire rescue team implements strict operational safety order control at the fire scene. Every firefighter who enters the fire scene is required to carefully check the reliability and air pressure of the air breathing apparatus. If the air pressure in the bottle does not meet the standard, it cannot be used. The safety officer will record the time when the firefighters enter the fire scene, and remind the firefighters to evacuate in time. For firefighters who cannot evacuate in time, the on-site headquarters should immediately organize emergency rescue. 2 Analysis of the reasons for the exhaustion of air breathing apparatus on the fire scene
Although firefighters have received professional and strict training, and the fire rescue team has strict management on the safe use of air respirators, the exhaustion of air respirators on fire cannot be prevented. The main reasons are as follows:
2.1 The use time of air respirator is short
According to the test of Du Xin and others of the former Armed Police College, the 6.8L air respirator can be used for an average of 50 minutes in normal walking (1.5m/s) when wearing a fire fighting suit and an initial pressure of 30 Mpa in a non-fire environment. Jogging can use an average of 22.1min (2.74m/s). The oxygen consumption of climbing stairs is 2.72 times that of walking on flat ground, and the oxygen consumption of descending stairs is 1.87 times that of walking on flat ground. In the fire environment, firefighters are highly stressed, the operational load is high, the human body is affected by high temperature, and physical energy consumption increases, and firefighters often need to climb and go down stairs, and the use time of air breathing apparatus will be further shortened. At the same time, there are obvious differences in the individual oxygen consumption rates among different people.
Due to the limited use time of air respirators, firefighters have a very short working time in the fire scene. The direction of travel, fire fighting and rescue, and evacuation must be very clear. The action is very decisive, and there is almost no room for error. Once there is a gap between the fire situation and the forecast , or a certain combat link encounters an emergency and is delayed, the firefighters will face the pressure of insufficient air supply of the air breathing apparatus, and every minute of delay may bring serious consequences.
2.2 The fire scene is complex and changeable
Fire-fighting and rescue is a high-risk post, and the environment of the fire scene is changing rapidly. With the development of society and economy, all kinds of new buildings and new technologies continue to emerge, high and low (high-rise buildings, underground buildings, large-scale complexes, petrochemical enterprises) fires increase, and new industrial and commercial building fires have large fire loads, large fire areas, There are many types of materials and high density of personnel. When firefighters attacked in close combat, they were often unable to evacuate as planned or the evacuation time exceeded expectations due to sudden changes in the fire situation and new risks and situations; the originally planned evacuation route was blocked due to local collapses, explosions or changes in the direction of fire spread; The large building area and complex structure may cause firefighters to lose their way in the fire scene, etc., which may cause the air in the respirator to be exhausted before the personnel are completely evacuated. 3 Emergency measures after the respirator air is exhausted
When the air in the respirator is about to run out, firefighters will be under great psychological pressure and must find a safe exit and leave the dangerous area in a short time. Once you can’t get out of the danger area in a short time, you will face the threat of suffocation. When it is found that the air in the respirator is about to run out, the following measures should generally be taken:
3.1 Remain calm and exercise strict breathing control When assessing that the remaining air volume is not enough to safely evacuate the fire, do everything possible.
May prolong the use time of residual gas. Firefighters should control their emotions, keep calm, stay away from high temperature and danger as much as possible, strictly control their breathing, and avoid unnecessary air consumption. Any impulsive and blind movement will speed up the consumption of oxygen and lead to a faster crisis. If you can’t keep calm, it is easy to make mistakes in decision-making and miss the chance to escape. Keeping calm is very important for firefighters to escape from the plight, and the consumption is 1.87 times that of traveling on flat ground. In the fire environment, firefighters are highly stressed, the operational load is high, the human body is affected by high temperature, and physical energy consumption increases, and firefighters often need to climb and go down stairs, and the use time of air breathing apparatus will be further shortened. At the same time, there are obvious differences in the individual oxygen consumption rates among different people.
Due to the limited use time of air respirators, firefighters have a very short working time in the fire scene. The direction of travel, fire fighting and rescue, and evacuation must be very clear. The action is very decisive, and there is almost no room for error. Once there is a gap between the fire situation and the forecast , or a certain combat link encounters an emergency and is delayed, the firefighters will face the pressure of insufficient air supply of the air breathing apparatus, and every minute of delay may bring serious consequences.
2.2 The fire scene is complex and changeable
Fire-fighting and rescue is a high-risk post, and the environment of the fire scene is changing rapidly. With the development of society and economy, all kinds of new buildings and new technologies continue to emerge, high and low (high-rise buildings, underground buildings, large-scale complexes, petrochemical enterprises) fires increase, and new industrial and commercial building fires have large fire loads, large fire areas, There are many types of materials and high density of personnel. When firefighters attacked in close combat, they were often unable to evacuate as planned or the evacuation time exceeded expectations due to sudden changes in the fire situation and new risks and situations; the originally planned evacuation route was blocked due to local collapses, explosions or changes in the direction of fire spread; The large building area and complex structure may cause firefighters to lose their way in the fire scene, etc., which may cause the air in the respirator to be exhausted before the personnel are completely evacuated.
3 Emergency measures after the respirator air is exhausted
When the air in the respirator is about to run out, firefighters will be under great psychological pressure and must find a safe exit and leave the dangerous area in a short time. Once you can’t get out of the danger area in a short time, you will face the threat of suffocation. When it is found that the air in the respirator is about to run out, the following measures should generally be taken:
3.1 Remain calm and exercise strict breathing control When assessing that the remaining air volume is not enough to safely evacuate the fire, do everything possible.
May prolong the use time of residual gas. Firefighters should control their emotions, keep calm, stay away from high temperature and danger as much as possible, strictly control their breathing, and avoid unnecessary air consumption. Any impulsive and blind movement will speed up the consumption of oxygen and lead to a faster crisis. If you can’t keep calm, it is easy to make mistakes in decision-making and miss the chance to escape. Keeping calm is very important for firefighters to escape from dilemma, and it is helpful for firefighters to use all available conditions to increase the chance of escape. However, a calm mind and good breathing control are subject to the rigid constraints of physiological limits, and effective equipment is still urgently needed to provide protection.
3.2 Call for help in time and take appropriate measures to wait for rescue
When judging that the respirator is not enough to support safe evacuation, firefighters should not hesitate to send out a distress message, and send it at least three times so that the commander and comrades can receive the distress message. The distress information should include the department title, name, exact location (or the last location that can be determined) and the situation of distress. Then, according to the actual situation on the scene, decide whether to stand still and wait for rescue, or find an exit to a safe location and wait for rescue. In general, in residential buildings, it should be as close as possible to the external windows. If there is no external window nearby, it should be moved as far as possible to a relatively safe, easy-to-search, and clearly marked location for search and rescue personnel to find.
The problem with waiting for rescue is that the speed of emergency rescue is very limited. It is very fast for the search and rescue team to find the person in distress in 5-10 minutes in a dark environment. The time required for emergency search and rescue often exceeds the rescue window time. Under the pressure of running out of air, it is very difficult for firefighters to stay calm and often fail to make correct decisions, including determining their location and moving to a suitable location to wait for rescue, thereby exacerbating the dilemma.
3.3 Filtering the air with combat suits
After the air in the air respirator is exhausted, it is undoubtedly the worst choice to take off the mask and directly expose to the smoke of the fire. In an emergency, you should lean over and crawl on the ground. You can unplug the quick connector of the air supply valve and the air supply pipe, and insert it into the combat suit from the neck. On the one hand, you can use the air in the combat suit to supply breathing. Heavy combat suits can act as a simple air purifier. It is also possible to remove the air supply valve and directly cover the air intake of the mask with a combat suit or hood for air filtration.
Prostrate yourself on the ground to help firefighters get oxygen. According to a statistical study by Yale University, in a fire, when the oxygen content of the ceiling is only 8.7%, the oxygen content of the ground is still 19%).
The problem with using combat suits to filter air is that it can only play the simplest filtering role, cannot filter poisonous gas, and has very limited protection.
4 Design of emergency equipment after breathing apparatus air is exhausted
4.1 Basic structure of emergency equipment
4.1.1 Material selection
Emergency equipment can choose portable compressed oxygen or filter-type anti-virus materials. If the compressed oxygen is not properly packaged and protected, it will bring safety hazards, and the gas cylinders that can provide sufficient safety protection in the fire scene are not light in weight, small in size, and inconvenient to carry. Therefore, it is more practical to use filter-type anti-virus materials.
4.1.2 Basic structure
There are two ways to breathe through the filter type anti-virus material: one is to connect the quick interface of the air supply valve air supply pipe to the filter type anti-virus material for breathing; the other is to directly connect the filter type anti-virus material to the air inlet on the mask for breathing .
Breathing through the quick interface of the air supply pipe of the air supply valve is simple and quick to operate, but because the air supply valve is equipped with a decompression device, the breathing resistance through the air supply valve under normal pressure is very large, and the body is uncomfortable and difficult to use continuously. It is the most scientific choice to put the filter-type anti-virus material into a special container to make a canister, and design a standard interface matching the respirator mask on the can body. The design of the canister is the same as that of the gas mask, and the design standard of GB 2890-2009 “Respiratory Protection Self-Priming Filter Gas Mask” is applicable.
The canister includes a filter layer, an adsorption layer and a chemical treatment layer. The filter layer is composed of high-efficiency filter cotton and ultra-fine glass fiber or other synthetic materials, the adsorption layer is activated carbon, and the chemical treatment layer uses different detoxification agents for different poisonous gases. Generally, special activated carbons are loaded with targeted detoxification agents without a separate chemical treatment layer. Figure 1 shows a schematic diagram of the structure of a common canister.
4.2 Design points of the canister
Life-saving canisters for firefighters should have higher requirements than ordinary civilian canisters.
4.2.1 Strong anti-virus ability
Ordinary fire canisters can filter out 99.99% of smoke and absorb toxic vapors and some toxic gases. CO cannot be adsorbed, and CO can be oxidized to non-toxic CO2 by special chemicals. When using, the oxygen concentration in the environment is required to be no less than 18%. Considering the complexity of modern fires and the diversity of firefighters’ work scenarios, the canister should be designed with a composite multi-functional filter for firefighter protection to filter and process more types of poisonous gases.
4.2.2 The use should be safe and convenient, light in weight, small in size, and easy to carry
The weight of ordinary canisters is generally not more than 300g, which is convenient, compact and easy to carry. The design of the multi-functional filter for firefighters should also strike a balance between protection performance and portability. The total weight of the canister should be controlled within 500g to facilitate portability and avoid extra burdens for firefighters in combat. The canister body of the canister should be sturdy and strong, with fireproof performance, and it is safe and reliable to use in the fire field.
When the air in the respirator is exhausted, the firefighter can use the canister to switch to the filtering protection mode, and then discard the rest of the air respirator (gas cylinders, back support, etc.)
Escape fast.
4.2.3 The protection time and shelf life should be longer
Generally, the protection time of the canister should not be less than 30 minutes, so as to provide sufficient escape time for firefighters. The shelf life of the canister under sealed storage should not be less than 5 years to reduce the cost of use.
5 The necessity of setting up a canister as emergency equipment
5.1 Urgent needs in reality
Based on the high-risk nature of firefighting and rescue operations, the situation of air exhaustion of respirator cannot be completely avoided. As mentioned above, conventional emergency measures can play a very limited role, and in a short period of time, the use time of air respirator cannot be significantly improve. Therefore, in addition to the conventional emergency measures, it is necessary and urgent to design backup emergency equipment for firefighters that can play a greater role.
At present, the canister is not included in the firefighter’s personal protective equipment standards, and where conditions permit, it should be tested first to accumulate experience and data.
5.2 Powerful practical functions
When firefighters are evacuating, in most cases they are not necessarily in the most dangerous areas. When the respirator air is exhausted, the canister is sufficient to provide life safety protection. Even in smoke-covered areas, the use of a canister may still not prevent injury when the respirator is depleted of air, but immediate death may occur if the canister is not used.
According to the statistical research of relevant research institutions, the oxygen concentration at the floor of most fire sites is higher than 18%, which is in line with the use conditions of the canister. Even in an environment where the oxygen concentration is lower than 18%, the threat of toxic gases such as CO to people is much higher than that of hypoxia. In a hypoxic environment, the human body can barely support for a period of time, but in the face of poisonous gas, the human body can support it for a much shorter time.
The canister should only be used in the most urgent situations and does not conflict with the use of air respirators. Canisters are equipped to provide firefighters with an alternate chance of escape in the most critical situations, and canisters are not a substitute for breathing apparatus. However, no matter the circumstances, when the respirator air is exhausted, the canister will protect the life of the firefighter without any toxic effect. And in most cases, this protection is still very effective, and the canister has a strong practicality.
6 Summary
Using filter-type anti-virus materials, at the most critical moment, the firefighter’s positive pressure air respirator can be quickly switched to a gas mask, so as to strive for the last chance for firefighters to escape. There have been similar explorations abroad, but there is no research in China. and application. Under the existing technical conditions, the use time of the air respirator cannot be significantly improved in a short period of time, and the air exhaustion of the respirator on the fire cannot be prevented. The use of a canister is a very wise choice.
The canister is small in size and light in weight, so it will not be a burden for firefighters, but it can provide respiratory protection for firefighters at the most critical moment. As the last resort and reliance for firefighters to escape from the fire, the application and promotion of “canisters” is of great value to protect the lives of firefighters, and it is necessary and urgent.
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