In fire fighting and rescue operations, firefighters fire protective clothing to protect the lives and safety of firefighters . It is the body for firefighters and other parts of the upper and lower torso conventional thermal protection of personal protective equipment , is the firefighter 's " Body armor ." However, the fire protective clothing thermal protective performance better, the total heat loss is lower. When confronted takes a long time , high-intensity combat scene of the fire , firefighters produce a lot of heat will quickly accumulate in biological fire protective clothing inside , to a certain extent , affect the physical and mental health of firefighters . Therefore, the experts expressed concern about use of fire protective clothing for firefighters ' health and safety. On fire protective clothing are breathable performance impact for firefighters , and describes some of the ways to improve permeability , for reference.

  
1 permeability and fire protective clothing
  
1.1 The concept of permeability
  
    Permeability is within a unit area per unit time through the layers of clothing quality steam to describe . To fire protective clothing , for example, water vapor molecules penetrate the layers of clothing depending on the speed firefighters fire protective clothing and the skin surface between the air and the water vapor concentration outside ( or humidity ) difference , but also by the physical fabric of resistance . Differences in turn depends on the moisture firefighters exercise intensity ( exercise intensity the greater the sweat out more ) and in which the climate. Resistance of the garment fabric material and its thickness used in a high performance . Generally, the thicker the fire protective clothing , thermal protective performance is stronger, while the breathable clothing worse .
  
1.2 Structure and fire protective clothing permeability
   
    fireproof clothing is the outer layer , waterproof breathable layer , insulation layer, comfortable layer multilayer composite made of fabric . Where: outer fabric has a high flame and thermal protective performance , defense and high-temperature flame ; waterproof breathable layer is located between the outer layer and the insulating layer , play to prevent water penetration to the insulation layer while discharging steam effect; insulating layer having a high temperature insulation effect, so that firefighters and radiant heat from heat damage ; comfort layer primary role is to firefighter wearing more comfortable. Multilayer structure makes fire protective clothing has good flame retardant, heat insulation, anti-radiation heat penetration properties, but at the same time fire protective clothing permeability will be weakened, and with the increase in the weight of fire protective clothing , so firefighters produce more bio- heat . This excess heat so that the body 's temperature rises , an impact on the health of firefighters .
  
2 fire protective clothing for firefighters permeability effects
  
2.1 physiological effects
  
    Body temperature regulation center in the hypothalamus , in which under the control of heat production and heat dissipation in dynamic equilibrium , can maintain normal body temperature . In other high-temperature environments fire movement , metabolism acceleration, increased heat production , the body will help firefighters skin blood vessels to dilate , blood flow acceleration, increased secretion of sweat , rapid breathing , etc., the heat generated by the body through the fire protective clothing service multilayer structure surface , by radiation , conduction, convection and evaporation heat , etc. , in order to maintain the temperature within the normal range . According to the research , the human circulatory system epithem thermal conductivity values ​​can be increased 5-6 times at this time , which is called thermal stress . Organisms have this stress ability , to ensure the survival of the thermal environment . But people's ability to heat stress is limited, but also has large individual differences . If firefighters fire protective clothing ventilation cooling performance is not good , and exercise in a hot environment for too long , more than the individual's ability to heat stress occurs as the hypothalamus perspiration central disorder , the body can not evaporate through perspiration heat , so that the body accumulates too much heat , causing firefighters appeared surface temperature, profuse sweating , shortness of breath , rapid heart beat, pulse rate and other conditions. If not timely mitigation and recovery will make firefighters dizziness , headache , palpitation , nausea, vomiting , etc. , in the hot summer environment , as well as firefighters may cause fainting or shock.
    According to the research , the impact of heat stress on firefighters also reflected in fire protective clothing with internal heat accumulation , profuse sweating will cause reduced blood flow , especially due to the reduction in plasma volume . Meanwhile, the body temperature causes vasodilation , vascular diameter increases , so that more blood deposition in the venous system , reducing the blood return to the heart , resulting in decreased blood flow or blood pressure, fast heart can not provide enough blood to meet the same muscle , heart and brain blood supply needs, likely to cause chest tightness, and heart attack . Heart disease is the leading cause of death firemen , USA firefighter death from heart disease each year accounted for roughly 40% of the total number of deaths over .
  
2.2 psychological impact
  
    Heat in a large number of fire protective clothing gathered firefighters fatigue causes rapid increase in strength dropped significantly decreased excitability , confusion , depression and other negative emotions rise , increasing the number of operational errors , the correct number decreased mental decline , velocity, decreased sensitivity and so on, seriously affecting the fire fighting performance.
  
3 Research and breathable performance improvement
  
    Given Fire fighting protective clothing for firefighters permeability health effects , scientists around the world in how to provide both high performance and a good air permeability protective fire clothing and research and efforts .
  
    Fire protective clothing Research and Improvement
  
    Finnish research institutions experimental verification of the fire protective clothing waterproof breathable layer on the permeability of the presence or absence of effects: the firefighters are divided into two groups, the first group contains a waterproof breathable wearing fire protective clothing layer , the second group without wearing waterproof and breathable fire protective clothing layers , the same two firefighting firemen , the first group of firemen skin temperature , sweat is much higher than the second set of firemen . The test results showed no waterproof breathable layer of fire protective clothing breathable performance better. However, the waterproof breathable layer fire protective clothing is essential for the structure . Fireman in fire fighting using large amounts of water and foam fire extinguishing agent to do if fire protective clothing undefended water permeable layer , waterproof will deteriorate the water through layers of clothing and firefighters skin contact, the impact on the health of firefighters , especially in the winter , it is possible to cause frostbite firemen . Waterproof breathable layer has a good waterproof performance, so fire protective clothing with waterproof breathable layer is necessary . In recent years , experts and research institutions has been developed and the more advanced waterproof breathable layer , such as the U.S. company has developed Gore PTFE membrane and eVent membrane , the water under the premise of improving fire protective clothing breathable performance.
  
    National Fire Protection Association standards , the total heat loss (TotalHeatLoss) to measure the permeability of clothing , clothing for firefighters to understand the impact of heat stress . The unit is : watts per square meter (W/m2). Total heat loss is higher, indicating that the more breathable fire protective clothing , with a heat and moisture to flow more external environment. 2007 edition of the NFPA1971 standards, four-layer structure fire fighting protective clothing shall not be less than the total heat loss 205W/m2. As a measure of thermal protective performance of protective clothing and the total heat loss TPP value THL exists between conflicting . If the thermal protective performance of protective clothing is excellent , its heat loss will be relatively low , which is relatively poor permeability , easy to make firefighters generate heat stress . Conversely, if the total heat loss of protective clothing is high , breathable performance is better, then the protective heat may not reach adequate protection requirements.
  
    In different circumstances , the firefighters focused on this contradiction will be different . When the firefighters in the conventional case , consider more of the total heat loss of protective clothing , that is breathable performance, while exposure to high temperatures deflagration when firefighters case , to consider more of a protective clothing thermal protective performance . Scientists around the world have long been in the field continue to explore, in 2008 DuPont scientists have invented a research, a good solution to this contradiction . The results of this study DuPont is one called Nomex? OnDemand insulation layer . In the conventional or normal conditions, the very thin insulating layer can maintain the state , with very good air permeability and flexibility , thereby reducing the firefighters in attendance may be encountered during heat stress . Use Nomex? OnDemand insulation layer fire suits , the total heat loss value of 260W/m2 (Kevlar / PBI outer fabric , CrosstechPJ waterproof breathable layer , Nomex? OnDemand insulation ) . When firefighters are due to deflagration High temperatures can cause severe burns when an emergency situation , Nomex? OnDemand will quickly activate thicken , making the heat insulation layer to retain more air , thus greatly improving the thermal protective performance of protective clothing .
  
    In addition, fire protective clothing should be designed from ergonomic considerations, based on regional differences, uses, firemen individual differences to design comfortable , targeted , fitting protective clothing. For example, in fire protective clothing coat axillary extension added at the connecting portion connected , so that firefighters more flexible and comfortable arm movement , thereby reducing the resistance due to overcome this part of the heat generated , more favorable to the protection of the health of firefighters .
  
3.2 Other improved methods
  
    Fire safety belt use improved method helps to improve breathability. For the protection of personal safety and convenience of firefighters firemen portable equipment considerations, and wearing the same old fire protective clothing , currently firefighters wearing fire protective clothing must still wear the waist belt of fire safety . However, different from the past is that the multilayer structure fire protective clothing and poor permeability characteristics determine its internal heat in part to rely on natural ventilation jacket hem , and fire safety belt wearing just plugging this important cooling channel , is not conducive to effective heat dissipation . It is understood that foreign firefighters wearing fire protective clothing worn when fewer fire safety belts, their usual practice is to firefighters will be required to carry the tools and self-rescue using ropes , ribbons, hooks , etc. placed in a dedicated device Messenger shoulders , coat hem can play a very good cooling effect .
  
    In addition , heat vest can also reduce fire protective clothing for firefighters poor ventilation effect . In the interior wearing fire protective clothing endothermic vests, heat exchange by forcing the physiological absorption heat accumulation , reduce the temperature inside the fire-fighting protective clothing to reduce physiological stress firefighters to protect their safety.