FAI Spring 2023 Process Safety News.ai

Evaluating the Flammability Hazards of Liquid Vapors The Flammability Team, Fauske & Associates With the increased number of reported fires and explosions, it is evident that there is an unacceptable absence of proper preventative measures and mitigative safeguards in place to reduce the number of fire-related incidents. Prior to scaling up a chemical process or working with a new chemical, it is critical to fully characterize the flammable properties of the chemical to get a strong understanding of the flammability potential and to set up the appropriate safeguards.

Before discussing flammable properties further, it is important to first understand the three general elements that are required for a fire or an explosion to occur: a fuel, an oxidizer, and an ignition source (Figure 1). Through removal of one of these elements, a fire/explosion will not occur (in most cases 1 ). Eliminating the ignition source is often not a practical method of prevention due to flammable vapors typically having very low minimum ignition energies (meaning they are very easy to ignite) as well as the likely existence of numerous different potential ignition sources (known and unknown). Therefore, moderating the fuel and oxidizer concentrations to avoid a flammable concentration of gases/vapors, otherwise known as the flammable region, is necessary for reducing the risk of a fire/explosion.

Figure 1: Fire Triangle

In the chemical industry, processing and handling of chemicals could result in the formation of a flammable or explosive atmosphere. For liquid chemicals, this may occur at temperatures other than at ambient conditions. Figure 2 shows the relationship between the flammable properties of a material and how they are related to temperature. As temperature increases, the vapor pressure of a material exponentially increases, and there becomes a point where the concentration of the vapor is sufficient to create a flammable atmosphere in air. This temperature is commonly known as the flash point (FP). In theory, the lower flammability limit (LFL) should intersect the vapor pressure curve at the

Figure 2: Temperature Effects on a Flammable Mixture (Crowl, 2003)

1 There are some unstable chemicals, like acetylene, which do not require an oxidizer to exothermally decompose.

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