METRICS · CONTAINMENT & SAFETY
Seal Leak Rate
VC-MET-403 — the measured air leak across sphere and airlock seals — direct evidence of seal integrity.
Current 3
Nominal 0–8
1 min cadence
PhytoSense Mesh
Definition
Seal Leak Rate is the volumetric air leak across a sphere or airlock seal (sccm — standard cm³·min⁻¹), measured by tracer-decay and make-up-flow methods. It is the direct mechanical complement to pressure differential.
Why it matters
Where differential shows the effect of a leak, leak rate shows its size. A rising rate localizes a degrading gasket before it costs containment and schedules seal maintenance before an alarm.
Formula
Q_leak = make-up flow at setpoint ΔP [sccm] Confirmed periodically by tracer-gas decay: Q = V · ln(C0/Ct) / Δt Reported per seal; rate normalized to the −35 Pa setpoint so readings are comparable across spheres.
Inputs
| Input | Detail | Source |
|---|---|---|
| Make-up flow | Flow to hold setpoint | PhytoSense Mesh |
| Tracer decay | Periodic confirmation | PhytoSense Mesh |
| Seal map | Seal-to-sphere assignment | CHLORA |
Units & Scale
sccm, integer, per seal, normalized to the −35 Pa setpoint. Increasing-is-worse; upper thresholds apply.
Sampling & Source
- Sampled every 1 minute from make-up flow.
- Confirmed periodically by tracer-gas decay.
- Normalized to setpoint for cross-sphere comparison.
Thresholds
Nominal · 0–8 sccm — tight seals
OK
Warning · > 20 — gasket service advisory
WARN
Critical · > 45 — seal failure
CRIT
Predictive maintenance. A leak rate trending upward over days schedules a gasket service before it degrades the pressure differential; the two metrics are alarmed together so a sudden rate jump with falling ΔP escalates immediately.
Recent Trend
Zone roll-up, last 14 sampling periods (current 3):
VC-MET-403 · 14-period trend (current 3)
Interpretation Guidance
| Band | Reading | Likely Driver | Action |
|---|---|---|---|
| 0–8 | Tight | Healthy gaskets | None. |
| 9–20 | Rising | Gasket wear | Schedule service. |
| 21–45 | WARN | Significant leak | Service; watch ΔP. |
| > 45 | CRIT | Seal failure | Isolate; breach review. |
Related Metrics
VC-MET-402
Sphere Pressure Differential
Pressure effect of leaks.
VC-MET-401Containment Integrity Index
Composite.
VC-MET-408HEPA Filter Loading
Filtration path.
VC-MET-409Decon Airlock Cycle Compliance
Airlock integrity.
Related SOPs
- Sphere & seal integrity — SOP Library.