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QD results: required, blast, frag

A QD analysis does not produce a single number. It produces a set of hazard-specific required distances — blast, fragmentation, sometimes thermal — and the Required value is whichever of those is the largest after all reductions. Reading the results panel correctly means seeing each hazard component independently, then reading off the governing value.

Learning objectives

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

  • Distinguish the Required, Blast, Frag, and Thermal values in the results panel
  • Identify which hazard governs in any given analysis
  • Trace any result back to the criterion entry and code that produced it using its analysis path and criteria path
  • Distinguish per-result paths from the PES/ES-level paths that resolve the analysis code

Required​

The Required value is the bottom-line answer — the separation distance the criteria require between this PES and this ES. It is the largest of the hazard-specific values after every applicable reduction (barricading, protective construction, attribute modifiers) has been applied.

This is the value plotted as the QD arc in Siter. When a user sees a single distance for a pair, it is this one.

Blast​

The blast distance is the separation needed to keep blast overpressure at the ES below the criteria threshold. It is computed from NEW, the K-factor (or formula) selected by the criteria path, and any reductions the path allows.

Frag​

The fragmentation distance is the separation needed to bound expected fragment-throw range. It is most relevant for hazard divisions 1.1 (with fragment-producing items) and 1.2 (where fragmentation is the primary hazard). For some hazard divisions this result is split between Primary Fragmentation (the high speed fragments from article casings) and Secondary Fragmentation (the lower speed fragments of buildings thrown by an explosion in the facility).

Fragmentation generally governs the required distance at lower NEWs. The exact convergence between Blast requirement and Frag requirement varies depending on criteria and the type of facility.

Thermal​

For 1.3 quantities (mass fire), thermal distance can be the governing hazard. For some criteria, the calculator surfaces it alongside blast and frag in the same results panel.

Tracing a result​

Every value in the results panel was produced by a specific path through the criteria flow, with a specific analysis code, after specific reductions. The engine returns two trace structures alongside each value so you can see exactly how the number was derived:

  • analysisPath — the human-readable, step-by-step narration of how that value was derived (see Tracing analysis paths)
  • criteriaPath — the list of formal criteria citations (sections, tables, notes) the engine touched while computing the value (see Criteria path)

The two are complementary. The analysis path tells you what the engine did; the criteria path tells you what authority justifies each step. Together they answer "how did the engine reach this number, and where in the criteria document is it justified?"

Each result carries its own pair of paths​

Per-hazard results — Required, Blast, Frag, Thermal, and the corresponding DQ values — each return their own analysisPath and criteriaPath. You can ask the same diagnostic question independently for each one:

  • "Why is Blast 400 ft?" → read the Blast result's paths
  • "Why is Frag 1,250 ft?" → read the Frag result's paths
  • "Why did Frag govern over Blast?" → read the Required result's path, which contains the cross-hazard comparison

A governingCriteria field on each result names the single criterion that produced the final value — the citation you would use when defending the result against external review.

Reading the analysis path: a worked example​

For a 1.1 PES at 1,000 lb NEW (AGM, light structure), an unrelated IHB ES, under DCMA (DoD Manual 4145.26), the Required result's analysis path reads:

QD Analysis, NEW: 1000lbs PES:AGSU to ES:IBD
Table AP2.T1. HD 1.1 IBD and PTRD
Note 4
For NEWQD < 30,000 lbs, the distance is controlled by fragments and debris.
30,000 lbs < NEWQD ≤ 100,000 lbs: d = 40*NEWQD^(1/3)
K/Q Factor
QD = 40 * 1000^(1/3) == 400
For exposures requiring HFD:
For all types of HD 1.1 NEWQDs in the range of 451 to 30,000 lbs

Read top-to-bottom as a procedure: identify the table → check Note 4 → apply the K-factor (yielding 400 ft for blast) → evaluate the HFD requirement (yielding 1,250 ft for frag) → take the larger. The final Required value (1,250 ft) is the HFD result, because it exceeded the K-factor blast value.

Reading the criteria path: the formal-citation companion​

The same result's criteria path:

Table AP2.T1.
Table AP2.T1., Note 4
Table AP2.T1., Note 4 - Blast
C5.8.1.7.
C5.8.1.7.2.
C5.8.1.7.2.1.

Each entry is a criterion the engine cited as it walked. The governingCriteria for this Required result is C5.8.1.7.2. — the HFD rule for 1.1 quantities in the 451-to-30,000 lb range, the criterion credited with producing the final 1,250 ft value.

Note that the governing criterion is not always the last entry in the criteria path. The path is the full set of criteria the engine touched while walking; the governing criterion is the specific entry that resolved the value. The engine returns both so you can see the walk and the verdict separately.

When you cite a result in a deliverable, the criteria path is the citation list you reproduce; the governing criterion is the one you call out as the controlling rule.

Per-hazard paths vs the Required path​

The Required path covers the engine's complete process — including the cross-hazard comparison that picks the governor. A per-hazard path covers only that hazard's calculation, before the cross-hazard step. In the worked example above:

  • The Blast result's path stops at QD = 40 * 1000^(1/3) == 400 and cites only Table AP2.T1., Note 4 - Blast
  • The Frag result's path covers the HFD evaluation and cites C5.8.1.7., C5.8.1.7.2., and C5.8.1.7.2.1.
  • The Required result's path contains both sub-calculations, because picking the governor is part of resolving Required

When you want to know why a particular hazard governed, compare the per-hazard paths against the Required path — the difference is the cross-hazard reasoning.

PES/ES analysis paths​

In addition to per-result paths, each pair returns a single PES-side and ES-side analysisPath that resolves the analysis code for the side (e.g., AGSU, IBD). These paths describe how attributes and type code combined to pick the entry node the per-hazard calculations then walked from. They sit one level above the per-result paths and are most useful when you want to understand which entry the engine started from before any explosive math happened.

Try it​

For a single PES → ES pair with 1.1 explosives, observe the Blast and Frag values independently. Increase NEW until the governor flips between them — the NEW value where this happens is a useful checkpoint, since it tells you which side of the threshold similar configurations sit on.

Then, for one of those analyses, open the Required result's analysis path and criteria path. Identify:

  1. The criterion entry the engine started from
  2. The blast formula it evaluated
  3. The HFD or fragment rule it evaluated
  4. The cross-hazard comparison that picked the governor
  5. The final governingCriteria citation

Repeat for the per-hazard Blast and Frag results and confirm their paths are subsets of the Required path — each per-hazard path stops at its own governor, while Required carries the comparison.