Sealing Flammable Liquids

We are often asked if it is safe to seal flammable liquids, that have extremely low flash points. There appears to be a misconception by the packagers of flammable liquids that the heat generated by the induction sealing process will somehow ignite their product. This confusion is caused by insufficient knowledge of the induction sealing process and the variables involved in determining if a flammable product will ignite.

Because the induction sealing process results in heat being generated in the aluminum innerseal that can reach several hundred degrees Fahrenheit, there is the false fear that this will ignite the product. This fear is the result of a misconception concerning the term "flash point."

This confusion is the result of not understanding the difference between flash point and autoignition temperature (AIT). Flash point is the temperature where a product develops vapors. This is not the temperature where the product will burst into flames. This means, a product like acetone, which has a flash point of 70 degrees Fahrenheit will begin to release vapors when it reaches this temperature. However, this is not a temperature that will support product combustion. A product will not ignite until it reaches its autoignition temperature, which in the case of acetone, is 869 degrees Fahrenheit. Normally the autoignition temperature is several hundreds of degrees higher than the flash point temperature. While the temperature of the foil innerseal may reach temperatures of several hundreds of degrees Fahrenheit, it will always be well below the autoignition temperature of the product being packaged.

Three conditions must be present for combustion to occur. First there must be fuel. This can be the product itself, or its vapors. Next, the fuel must be brought to it's autoignition temperature. The third condition to support combustion is the presence of oxygen.

When a flammable liquid is being sealed at room temperature, it is safe to assume it will reach its flash point, resulting in vapors being formed. These vapors will displace the oxygen in the head space of the container and when the container is capped, these vapors will be contained in the head space. The head space, filled with the vapors of the flammable liquid, become too rich to burn since there is not enough oxygen left to support combustion. In the extremely unlikely event that the product reached its autoignition point, the product would still not be able to burn.

To the best of my knowledge, in the over thirty years since induction sealing has been used, I have never heard of a problem as a result of sealing flammable liquids. The danger of a fire, caused by the induction sealing process, when sealing flammable products, is very low.

Understanding flash-point versus auto-ignition temperatures, shows why induction sealing flammable liquids is a generally safe procedure.