The nomogram works by computing the electrostatic energy (Ue) stored in a capacitive model for a practical system. On the energy scale of this nomogram are marked values of minimum electrostatic discharge energy (MIE = Minimum Ignition Energy) known to ignite typical flammable materials, such as gas/air mixtures, vapors, and dust suspended in air. A user can quickly assess the risk by comparing the calculated value of Ue to MIE . The equation for capacitive energy is:
where C = system capacitance (Farads) and V is voltage (Volts), both of which typically are estimated using a worst-case approach. The determination of MIE is sometimes very difficult, but once a value is known, a safety engineer can assess the risk of ignition in an industrial plant or commercial facility. If the calculation reveals that
then the likelihood of an ignition is low. Conversely, if
then appropriate actions are called for to reduce the hazard.
To view the online interactive nomogram based on the above equation,
Note the typical values for C, MIE, and V displayed for
convenience on the various scales.
NOTE: For convenience in certain situations, this particulate nomogram contains an extra scale for calculating the charge Q (in Coulombs). The relationship betweeen charge and the other variables is