# Blast Pressure Calculator Guide (Level 2)

### What is it?

The arc blast pressure calculator theoretical formulae developed by Ralph H Lee, published in his paper “Pressures Developed by Arcs” in 1987. There is much debate about how Lee’s theoretical formulae can be interpreted in the real world, but this is still widely cited by engineers when calculating the severity of the blast hazard. More information is given in Chapter 2: What is Arc Flash.

### Why would you use it?

The Blast Pressure Calculator provides a method to determine and compare blast pressure under relative scenarios. Whilst there is caution about the absolute accuracy in real life situations, it serves as an educational tool and could also highlight extreme danger.

### How do you use it?

This calculator uses his formulae to give an initial blast pressure figure. As can be seen in Figure 14.19 of the calculator.

###### Figure 14.19 Blast Pressure Calculator

The following details the data entry values that will be required.

##### Arcing current (kA)
Enter the calculated arcing current in kA. (Not the prospective short circuit current).

##### Working distance (metres)
Enter the working distance which is the distance from the prospective arcing source to the person’s torso in meters.

##### Blast Pressure
The initial blast pressure is given in Kilopascals, lbs/ft2, N/m2 and Atmospheres all of which can be selected via the dropdown list. When doing so, the value produced will automatically update to the associated unit.