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Barricading

A barricade between a PES and an ES can reduce the required separation distance — but the reduction is only available when the criteria path allows it. Knowing exactly when a barricade earns the reduction (and when it does not) prevents the most common modeling mistake on the calculator: assuming a barricade always helps.

Learning objectives

By the end of this lesson you should be able to:

  • Recognize criteria paths where adding a barricade changes nothing
  • Predict the analysis-code change a barricade should produce — or confirm that it should not

What a barricade does​

A barricade is an engineered intervening structure (or qualifying natural feature) that interrupts line of sight, high-velocity low-angle fragments, between a PES and an ES. The criteria treat an effective barricade as a discount on certain required distances — typically in IMD where intercepting fragments has a large impact on preventing simultaneous detonation.

Under DCMA, barricaded ILD drops from K18 to K9, and IMD from K11 to K6 when an effective barricade exists between two facilities.

Just stopping fragmentation, however, is not always enough of a reduction in risk. So under the 4145.26, barricaded ILD may only be applied between successive steps of the same operating line.

When barricading reduces required distance​

The reduction is conditional. Under DCMA it activates only when all of the following are true:

  • For Operating Locations the relationship between PES and ES is sameline (Same Operating Line)
  • For Storage Locations relationship is not pertinent.
  • The criteria path supports a barricaded variant — typically ILD or IMD, not IBD or PTRD (with the exception of NATO criteria)
  • The barricade itself meets the criteria's effectiveness requirements

If any condition fails, adding a barricade has no effect. The engine does not silently apply a partial reduction or warn that a barricade was placed in vain — it just walks the unbarricaded branch of the criteria flow.

When barricading does nothing​

Common scenarios where adding a barricade produces no change:

  • Parallel operating lines (related, not sameline) — unbarricaded ILD (K18) applies regardless. See the Barricaded related vs barricaded sameline exercise.
  • IBD or PTRD Exposure Type analyses — inhabited buildings and public transportation routes do not earn barricaded reductions under US criteria.
  • Fragmentation-governed results — barricades only have an impact on low-angle fragmentation. High-angle (or lobbed) fragmentation does not see a reduction in criteria with a barricade.

When a barricade produces no change, the criteria path or analysis path are the diagnostic. Open the analysis path and locate the step where the engine decided whether to apply the barricaded variant.

Try it​

For a worked walkthrough that demonstrates exactly when a barricade does and does not reduce ILD, see the Barricaded related vs barricaded sameline exercise. It is the canonical example of this pitfall and the fastest way to internalize the rule.