Some of the most common questions we hear from a refinery, TIC fuels testing, or terminal lab aren't about whether to run SQC: they're about how often. Specifically: does a precision or accuracy check actually need to happen every time a batch goes out the door, or is that just how it's always been done?
It's a fair question, and it comes up more than you'd think. A lab schedules a benzene precision check in BLISS SQC+ at 0700. Operations submits a blend for batch certification at 0900. Now benzene is being assessed twice within two hours, once on schedule, once because "that's the procedure before we certify." Multiply that across every regulated property on every batch, and a lab can end up running significantly more SQC than the regulation actually calls for.
If that sounds familiar, you're not alone, and you're not doing anything wrong. But it's worth understanding where the practice comes from, and where the actual regulatory line sits, so your team can make an informed decision about frequency rather than an inherited one.
Neither 40 CFR Part 1090 nor ASTM D6299 requires a precision or accuracy check to run in parallel with, or immediately before, batch certification. The performance-based measurement system (PBMS) frequency requirements in 40 CFR 1090.1375 prescribe how often precision and accuracy checks need to occur; they say nothing about proximity to a specific certification event.
Paraphrasing the frequency requirements:
That's the actual regulatory floor. Nothing in the framework requires re-running either check just because a blend happens to be ready for certification at a given moment.
It's a safeguard, not a requirement, and it's a reasonable one on its face. The logic goes: if an SQC check fails a week after it was last run, every batch certified during that window may need to be revisited. That's a real risk, and for some labs, testing precision immediately before certification feels like the safest way to avoid it.
The tradeoff is testing volume. If your lab is running a precision check once per shift and an accuracy check weekly, you are almost certainly well within the regulatory frequency window on your own schedule, without needing to layer a second check in front of every batch. Certifying "alongside batch" adds testing load without necessarily reducing risk.
This isn't a one-size-fits-all answer. The right frequency depends on your lab's own risk tolerance, your historical SQC performance, and how much testing capacity you have to spare. A few questions worth asking your team:
Every redundant SQC run is instrument time that isn't going toward new samples. On a lab running dozens of tests a day across multiple regulated properties, "just to be safe" testing at every batch certification can add up to a meaningful share of total lab capacity, additional cost and added wear on the analyzers.
This is exactly the kind of question that's hard to answer from a spreadsheet or a paper log, and much easier to answer with a system that tracks SQC scheduling, run history and TPI performance, all in one place. BLISS SQC+ tracks precision and accuracy check scheduling automatically, surfacing when a check is due, when it's still valid, and where testing may be duplicating coverage that's already in place.
Frequently Asked Questions
Does EPA Part 1090 require an SQC check immediately before every batch certification? No. 40 CFR 1090.1375 specifies precision and accuracy check frequency — 7 days or 20 non-QC runs for precision, 130 days for accuracy.
Is running SQC alongside every batch certification a bad practice? Not necessarily. It's a conservative internal convention some labs use as an added safeguard. It isn't required by ASTM D6299 or Part 1090, and it isn't inherently wrong, but it has tradeoffs and unintended consequences that must be carefully considered.
How often should a lab run precision and accuracy checks? Many labs settle on a daily precision (SQC) check and a weekly accuracy check, which comfortably covers the regulatory frequency windows. The right cadence depends on your lab's own risk tolerance and historical SQC performance. Note that labs running especially high volumes of tests may need a per-shift or other frequency for the precision SQC.
If your lab is asking similar questions about testing frequency, scheduling, or where SQC capacity is actually going, schedule a conversation with a Datacor SQC+ specialist — we're glad to help you think it through.