Fire can be said to be everyone's nightmare, not to mention the people in the fire. Light is easy to respiratory injury, serious words, easy to cause skin burns, and even lose their lives. Even if you are not in a fire, there may be danger in the vicinity of a fire.

However, the real deadly fire is often not the fire, but the invisible smoke from the fire. There are many components of flue gas, a large number of which are toxic and harmful gases, such as carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen oxides and so on. Among them, hydrogen cyanide (HCN) itself is extremely dangerous. After it is combined with carbon monoxide, the risk coefficient will increase exponentially, which will greatly threaten the life safety of rescue workers. Therefore, in the fire safety field, it is called "double gas".

Twin toxic gas was born as early as the 1970 s, when fire departments began to realize the hazards of inhaling toxic gases in smoke. As research progressed, it was discovered that the toxic gases emitted during the cleanup of the fire were equally dangerous. At present, the industry has gradually realized the long-term health hazards of these toxic gases, such as cancer risk.

In the past, household goods were mostly made of natural materials, such as cotton, wool and wood. But after the 1960 s, synthetic materials began to be widely used. Today, most furniture, carpets, bedding, clothing, household appliances, electronics and building materials are made of synthetic materials. These synthetic materials, when burned, release high concentrations of HCN and other toxic substances, especially insulating materials.

Because the synthetic material burns at a higher temperature and flashes faster, the release of HCN is also more rapid. The radiant heat generated by the fire rapidly heats the surrounding materials, triggering a quantitative decomposition reaction that spreads toxic gases throughout the building. The 2003 fire at a nightclub in West Wawwick, Rhode Island, USA, is a tragic example of quantitative decomposition. When the band played, the exothermic reaction triggered by the pyrotechnic device caused the non-compliant anechoic foam board to burn, producing a large amount of dense smoke containing HCN. Due to the inadequate sprinkler system in the building, the site became unbearable in just 90 seconds. Many of 462 people had difficulty escaping because of HCN/CO in the smoke, which eventually killed 100 people and severely burned or injured more than 200 people.

According to past statistics, smoke inhalation is the main cause of death in residential and commercial floor fires, not burns. According to the NFPA, smoke inhalation kills eight times as many people as burns. In the event of a fire, as the oxygen content decreases, the environment may contain high concentrations of carbon monoxide and other toxic substances. Moreover, the toxicity of smoke has nothing to do with its thickness, color or trajectory, so it is impossible to judge how much toxic gas is produced in the building by observing the smoke. Even light-colored smoke can contain deadly toxins. Although firefighters are exposed to harmful substances through both the lungs and the skin, inhalation by the lungs is 300 times more efficient than absorption by the skin.

Many people think that the gas killer in the fire is carbon monoxide and other well-known gases, but otherwise, HCN is often the most easily overlooked existence. Statistics show that in thousands of fires every year, HCN gas is a very important fatal factor. In fire smoke, HCN is dozens of times more toxic than CO.

Therefore, the National Institute for Occupational Safety and Health (NIOSH) has set a short-term exposure limit (TLV-STEL) of 4.7ppm for HCN, and workers must not be exposed to an environment exceeding this concentration for more than 15 minutes and must not be repeatedly entered into such an environment more than 4 times a day. The ACGIH (American Conference of Governmental Industrial Hygienists) has designated 4.7ppm as the Upper Exposure Limit (TLV-C) for workers, meaning that workers must never be exposed to more than this concentration. Shockingly, studies have shown that in common building structure fires, HCN concentrations often reach 200ppm, which is high enough to be fatal within 30 to 60 minutes! Because HCN is extremely toxic, symptoms such as dizziness, weakness and rapid heartbeat of firefighters after a fire may be related to HCN exposure. Many of the heart attacks and cardiac arrests that occur during or after firefighting can also be related to HCN. In addition, HCN can produce narcotic-like effects, leading to irrational and bizarre behavior that allows firefighters or victims to make potentially life-threatening decisions.

In order to protect the life safety of rescuers in a fire and to warn HCN gas in time in a fire, it is necessary to use special HCN gas detection sensors. At present, most HCN sensors on the market are based on electrochemical detection principle. The HCN sensor HCN-A1 Alphasense by the UK, which is represented by Shenzhen, can perfectly provide a safe rescue environment for firefighters, thus reducing rescue casualties.

The main parameters of the HCN-A1 are as follows:

Measurement range: 100ppm

Sensitivity: 45 ~ 85nA/ppm

Response time:< 70s

Linear range: 0 ~ 40ppm

Full range error: 4 ~ 8ppm

Overload: 150ppm

Resolution:<0.05ppm

Size:$20.2*16.5

Service life: 2 years

Storage period: 6 months