Fire Suppression, Sprinkler & Safety System Products worked example

Pressure Decay Margin with allowed pressure decay of 2.5 psi, bar, or kPa: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop allowed pressure decay to 2.5 psi, bar, or kPa, then walk the calculation through step by step. Calculate pressure-decay test margin by comparing allowed pressure loss with measured pressure loss.

The inputs for this scenario

  • Allowed pressure decay: 2.5 psi, bar, or kPa (the input this scenario stresses; the baseline uses 5)
  • Measured pressure decay: 2.8 psi, bar, or kPa (held at the documented default)
  • Reference decay limit: 5 psi, bar, or kPa (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Pressure Decay Margin = allowed pressure decay - measured pressure decay.
  • Pressure Decay Margin works out to -6 % at these inputs, and this is the headline figure for the scenario.
  • Pressure Decay Margin amount works out to -0.3 psi, bar, or kPa at these inputs.
  • Allowed pressure decay works out to 2.5 psi, bar, or kPa at these inputs.
  • Measured pressure decay works out to 2.8 psi, bar, or kPa at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where allowed pressure decay sits at 5 psi, bar, or kPa and the headline result is 44 %, this scenario comes in 114% below the baseline at -6 %.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to allowed pressure decay, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It's only as good as a controlled test: temperature swings, hold-time differences, and trapped air can move the measured decay, so an out-of-spec margin needs test-condition verification before you condemn a part.

Results at a glance

  • Pressure Decay Margin: -6 % (headline result)
  • Pressure Decay Margin amount: -0.3 psi, bar, or kPa
  • Allowed pressure decay: 2.5 psi, bar, or kPa
  • Measured pressure decay: 2.8 psi, bar, or kPa

Run it with your numbers

  • To rerun this with your own numbers, open the live Pressure Decay Margin calculator, set allowed pressure decay to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.