This is a ready-to-use worksheet for confirming that a depyrogenation tunnel’s belt speed setpoint actually delivers the residence (dwell) time through the hot zone that the lethality calculation assumes. It sits between OQ, where the belt’s speed control is qualified as a function, and the PQ endotoxin-indicator challenge, which depends on that speed-to-dwell relationship being verified rather than read off a control panel. Replace every <<FILL: ...>> placeholder with your own specifics. A filled specimen follows. This is educational reference content, not regulatory advice.
Why this worksheet exists
The FH lethality calculation and the endotoxin-indicator challenge both assume a container spends a known amount of time in the hot zone. That time is not the number on the belt-speed display; it is hot zone length divided by actual belt speed, and belt speed can drift from its displayed or commanded value as belts stretch, slip, or are driven by a controller with its own calibration tolerance. This worksheet closes that gap by physically timing product transit through the hot zone at more than one speed setpoint and comparing the measured residence time to what the validated minimum requires, so the PQ challenge is placed against a verified relationship rather than an assumed one.
Header
| Field | Entry |
|---|---|
| Worksheet number | <<FILL: FORM-ID>> |
| Parent protocol / OQ or PQ reference | <<FILL>> |
| Equipment / asset ID | <<FILL: tunnel name / asset ID>> |
| Hot zone length | <<FILL: e.g. 1.2 m>> |
| Belt speed control range | <<FILL: e.g. 60 to 200 mm/min>> |
| Validated minimum residence time (from PQ / FH basis) | <<FILL: e.g. not less than 3.5 minutes>> |
| Timing method | <<FILL: stopwatch on a marker container / photoelectric timing gates / logged encoder data, cross-checked>> |
| Date | <<FILL>> |
Field definitions
| Field | Format | Required | Who | When |
|---|---|---|---|---|
| Belt speed setpoint tested | numeric, mm/min or equivalent | Yes | Validation engineer | Per run |
| Commanded vs. displayed speed | numeric | Yes | Validation engineer | Per run |
| Marker container / method | text | Yes | Validation engineer | Per run |
| Time entering hot zone | timestamp | Yes | Validation engineer | Per run |
| Time exiting hot zone | timestamp | Yes | Validation engineer | Per run |
| Measured residence time | numeric, minutes | Yes | Validation engineer | Calculated |
| Calculated residence time (length / speed) | numeric, minutes | Yes | Validation engineer | Calculated |
| Agreement between measured and calculated | percent difference | Yes | Validation engineer | Calculated |
| Margin to validated minimum | numeric, minutes and percent | Yes | Validation engineer | Calculated |
| Pass / fail | Yes/No | Yes | Validation engineer | Calculated |
Instructions
- Confirm the hot zone length used in the calculated residence time is the physical length the load is actually exposed to lethal temperature (not the full tunnel length, which includes the infeed and cooling zones), and reference the drawing or as-built measurement that supports it.
- At each belt speed setpoint to be tested, run a marker container (or a string of containers at the worst-case load density) through the tunnel and time its transit through the hot zone directly, entry to exit. Do not rely solely on the belt-speed display; a physical or independently logged timing method is the point of this worksheet.
- Calculate the expected residence time as hot zone length divided by belt speed, using the same units, and compare it to the measured value. A large disagreement between measured and calculated residence time (beyond the tolerance your equipment SME sets in advance) is itself a finding: it means the display, the controller calibration, or the assumed hot zone length is wrong, and it must be resolved before the PQ challenge is placed against this relationship.
- Test at least the maximum qualified belt speed (shortest dwell, the least lethal condition, which is what the PQ worst-case cycle uses) and the minimum qualified belt speed. Testing an intermediate speed is recommended where the speed-to-dwell relationship needs to be shown linear across the operating range, not just at the two extremes.
- Compute the margin between the measured residence time at maximum belt speed and the validated minimum residence time the FH basis requires. A margin at or below zero means the tunnel cannot meet its own validated lethality assumption at its fastest qualified speed; do not proceed to the PQ challenge until this is resolved.
- Record any belt speed drift observed over the course of testing (for example, a speed that reads correctly at the start of a run and drifts under load) as a separate finding, since routine production runs longer than a single timed transit.
Calculation method
Calculated residence time (minutes) = hot zone length / belt speed, converted to consistent units.
Percent difference between measured and calculated = ((measured minus calculated) / calculated) x 100.
Margin to validated minimum (at maximum belt speed) = measured residence time at maximum speed minus validated minimum residence time.
Residence time verification table
| Belt speed setpoint | Commanded/displayed speed | Marker/method | Entry time | Exit time | Measured residence time | Calculated residence time | Agreement | Pass/Fail |
|---|---|---|---|---|---|---|---|---|
<<FILL: maximum qualified>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> |
<<FILL: intermediate>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> |
<<FILL: minimum qualified>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> | <<FILL>> |
Decision
| Item | Result |
|---|---|
| Measured residence time at maximum belt speed >= validated minimum residence time | Yes / No |
| Measured and calculated residence times agree within tolerance at every tested speed | Yes / No |
| Belt speed stable (no significant drift) across the timed runs | Yes / No |
| Overall | Pass / Fail |
| If Fail, deviation reference | <<FILL: number or N/A>> |
Retention
Retain with the parent OQ/PQ protocol for not less than <<FILL: retention period>>. This worksheet is the evidence that the belt-speed-to-residence-time relationship used in the FH calculation and the routine cycle parameters was independently verified, not assumed from the equipment’s control display.
Filled specimen
Example for tunnel DPT-02, hot zone length 1.2 m, belt speed control range 90 to 150 mm/min, validated minimum residence time 3.5 minutes (from the PQ FH basis), timing method a marker vial tracked by two photoelectric gates at hot zone entry and exit, cross-checked against a handheld stopwatch.
| Belt speed setpoint | Commanded/displayed | Method | Entry time | Exit time | Measured residence | Calculated residence | Agreement | Pass/Fail |
|---|---|---|---|---|---|---|---|---|
| 150 mm/min (max, worst case) | 150 mm/min | Photoelectric gates, marker vial, 3 replicate runs | 10:02:00 | 10:10:00 (mean of 3) | 8.0 min | 1200 mm / 150 mm/min = 8.0 min | 0.0 percent | Pass |
| 120 mm/min | 120 mm/min | Same method, 2 replicate runs | 10:22:00 | 10:32:00 | 10.0 min | 1200 / 120 = 10.0 min | 0.0 percent | Pass |
| 90 mm/min (min) | 90 mm/min | Same method, 2 replicate runs | 10:41:00 | 10:54:20 | 13.3 min | 1200 / 90 = 13.3 min | 0.0 percent | Pass |
Decision: Measured residence time at maximum belt speed, 8.0 minutes, exceeds the validated minimum of 3.5 minutes with a margin of 4.5 minutes. Measured and calculated residence times agree within 0.0 to 0.3 percent at every tested speed (small rounding differences omitted from this table for clarity). No belt speed drift observed across nine timed runs. Overall: Pass. The 150 mm/min setpoint used as the PQ worst-case parameter is confirmed to deliver the residence time the FH basis assumes, so the EI challenge at that setpoint is placed against a verified relationship.
Note what this worksheet is not: it does not replace the EI biological challenge. It confirms the mechanical assumption (time in the hot zone) that the FH calculation and the challenge both depend on. A tunnel that passes this worksheet but has never run the EI challenge is not qualified; the two lines of evidence, mechanical and biological, are both required.
Common inspection findings this worksheet prevents
- Belt speed assumed from the control panel display with no independent physical timing to confirm actual transit through the hot zone.
- A hot zone length used in the FH calculation that does not match the as-built or as-measured hot zone, silently overstating residence time.
- Belt speed qualified once at installation and never re-verified, while belt wear or controller drift over years of operation goes uncaught between requalification cycles.
- The PQ worst-case cycle run at a commanded belt speed that was never independently confirmed to produce the dwell time the acceptance criteria assume.
How to adapt this worksheet
- Set your hot zone length, belt speed range, and validated minimum residence time from your own equipment drawings and PQ FH basis.
- Choose a timing method appropriate to your equipment (photoelectric gates, a logged encoder cross-checked against a manual timer, or a stopwatch on a marker container) and state it in the header.
- Test at minimum the maximum and minimum qualified belt speeds; add an intermediate point if you need to demonstrate linearity across the range.
- Feed a Fail result into your deviation process before proceeding to the PQ endotoxin-indicator challenge; do not run the biological challenge against an unverified mechanical assumption.