We are surrounded by all kinds of gases and vapors and typically think nothing of it. The atmosphere around us includes the chemicals we work with every day. One of the largest risks to people and property in the chemical process industry is unintended deflagration/detonation. When working with a process containing flammable chemicals, it is critical to have accurate and reliable information on the flammable properties. This information is utilized primarily in two different ways depending on the limitations of the process or environmental conditions. The first use of the information is prevention. This is typically done by utilizing the flammable limits (ASTM E918) or limiting oxygen concentration (ASTM 2079) information to ensure a flammable environment is not created. The other use is mitigation. When using a mitigative approach, the process may intentionally operate inside the flammable region. If this is the case, the system needs to be designed for a possible deflagration event. To design mitigation systems, explosion severity needs to be determined with a high level of certainty to ensure the safety of people and property.
Figure 1
Having the right tools to assess flammability hazards of vapors and gases in dynamic systems is essential to developing the best prevention and mitigation plans. One of the most robust tools for evaluating a system in flux is a flammability triangle as seen in Figure 1. These are tertiary diagrams which give a full picture of the flammability risks associated with mixtures of a particular fuel, oxidizer, and inertant. With these diagrams it is quick and easy to assess which mixtures will approach or enter the flammable region. Additional information that is gained from the underlying test campaigns are flammability limits and limiting oxidizer concentration. Flammability triangles eliminate the need for reevaluation of mixtures as compositions change. As long as the components, pressure and temperature remain constant, flammability triangles can be utilized to assess and tailor composition to avoid the flammable region.
The Minimum Ignition Energy (MIE) is incredibly helpful in assessing the need for electrical protection utilizing explosion proof electrical equipment and grounding. Some gases and vapors have very low MIE values as seen in Table 1. To put these energies into perspective Table 2 shows some common ignition sources with their respective energies. Even a static discharge of someone walking across the carpet is enough energy to ignite a variety of vapors and gases. It is easy to default to electrical protection if a flammable gas or vapor is present, but that is not always the case. The use of unnecessary electrical protection can lead to higher cost and difficult design modifications. Though components such as hydrogen and propane have incredibly low energy thresholds for ignition, many of the newer environmentally friendly refrigerants are being sold as having very high ignition energy requirements well over 1 J and as high as 10 J. It is important to have the right information to assess if enhanced electrical protection is required, and for new refrigerants we offer specialized custom testing to make sure the full safety picture is revealed.
