Module A21
After finishing this online course you will be an expert on the risk of ventricular fibrillation (VF) as a result of body currents. This risk depends on the current magnitude, current path, duration and time of occurrence. Studies have been performed by different persons over time. This module is set up to explain you all about the history and establishment of the different curves in IEEE Std80 and IEC.
Then, background information of the body impedance will be provided. The body impedance is the sum of the internal impedance of the human body and the impedance of the skin. They depend on current path, touch voltage, duration of current flow, frequency, degree of moisture of the skin, surface area, pressure exerted and temperature.
Finally, there are different types of additional resistances that may be applied during the investigation of the tolerable (touch) safety of a potentially hazardous situation. In the end, the total electrical chain can be investigated.
Tools
Five excel tools will be available for you to download and use; two tools containing the curves from IEEE and IEC that describe the relationship between the maximum tolerable body current and the duration of a shock. The first tool contains the classic curves, determined using different methods (read from the graph, and described by formula’s), the second also contains new proposed (but not yet accepted) curves.
The third tool describes the body impedance as provided by IEC 60479-1. The fourth tool describes additional resistances as a result of surface treatment (using asphalt or gravel). The fifth tool combines all four together and provides you with calculated values, giving you the choice to select different methods and input criteria.
Prerequisites for the use of the tools: you will need a recent version of MS Office Excel with the option to run VBA macro’s. You will need to run these tools to complete the course. These tools may be changed or improved, which is easy to do if you have experience with Excel and VBA.
References: this online course on touch safety mainly refers to IEEE Std 80 and IEC 60479-1.
Key words: step and touch potentials; electrical safety; maximum tolerable body current; additional resistance; shoe resistance; duration; short circuit current
