Currently trying to calculate the alert and action levels for a purified water system after completing phase 1 of PQ

Using the following equations:

Alert Level = Average + 2 x Standard Deviation

Action Level = Average + 3 x Standard Deviation

when i use these equations, my action level for microbial count is well over the specifications (no more than 100 cfu/ml)

Is this normal? Does this mean my TVC counts are too high to progress to Phase 2 of the PQ?

Any suggestions on what to do with this information would be helpful.

Thank you

It means your out of control! Your ‘standard deviation’ (which influences sigma) is FAR too variable. It also means that you do not have a ‘normal distribution’ (common if we are talking microbes).

Thank you for your response.

So it would not be advisable to move onto Phase 2 of the PQ with this amount of variation then?

Would the phase 1 testing have to be repeated?

No, don’t move on. This is a prime example of using DMAIC (Define, Measure, Analyze, Improve, Challenge). Get in CONTROL!

It could be a simple as eliminating ‘deadlegs’ in your water distribution loop, where bugs can accumulate in still water. Is your water distribution loop heated?

The water piping/distribution system is maintained at ambient temperature and there is an online UV column installed in the water distribution loop prior to its distribution to user points.

Are alert and action limits for pH necessary to calculate using the above formula? Both my alert and action limits are above pH 7 when i calculate them out using my phase 1 sampling results.

A high SD may necessitate a pH meter that reads to 2 or 3 decimals points. Follow USP/EPA/APHA procedures which use ‘a saturated solution of KCL’.