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Pressure Safety valve sizing calculator for fire case for a gas filled vessel.
The calculated area is the minimum orifice area required to allow the discharge of gas. The actual orifice area is the next higher available area. Following table presents the standard orifices with their designating letters and corresponding area.
| Area (cm2) | Designating letter | Valve size (inch) |
| 0.71 | D | 1D2 / 1.5D2 / 1.5D3 |
| 1.26 | E | 1E2 / 1.5E2 / 1.5E3 |
| 1.98 | F | 1.5F2 / 1.5F3 |
| 3.25 | G | 1.5G3 / 2G3 |
| 5.06 | H | 1.5H3 / 2H3 |
| 8.3 | J | 2J3 / 3J4 |
| 11.86 | K | 3K4 / 3K6 |
| 18.49 | L | 3L4 / 4L6 |
| 23.2 | M | 4M6 |
| 28 | N | 4N6 |
| 41.2 | P | 4P6 |
| 71.2 | Q | 6Q8 |
| 103 | R | 6R8 / 6R10 |
| 168 | T | 8T10 |