UV Intensity Meter Calibration 1

[dtreacy]

We operate a 4 lamp UV disinfection unit on our purified water distribution loop.
During a 3rd party audit we were requested to calibrate the UV intensity meter and duty hour totaliser on the unit.
I have a number of questions regarding this:
1) Does anybody currently calibrate their duty hour totaliser and intensity meter?
2) How do you calibrate the intensity meter?
3) Who carries this work out?

Any help would be appreciated.

 

[MedicineEng]

That one is difficult. I already tought about that and I pray whenever I have an audit to not have a smart guy asking me that.
I really don't know if there is any intrument available in the market that you can use to assess if your UV lamp is in the 254nm wavelenght range. Besides that, as you know, you should not be exposed to that light since thsi wavelenght can have some effects in your DNA (that is why they kill bacteria).
What I usually do is follow the manual of the supplier to set the sensor and the alarm level.
How can you defend yourself? Well, calibrations are needed to prove that system under control and that you can trust in the readings that you receive from your system trough instrumentation. If you have a test/checking after a determinate instrument that proves the functioning of that specific component, your calibration might be waived. In this specific case, what I did was to install a sample point right after the UV light. With that, I can check if the UV is working properly or not by making a micro biological test. Then, you pass the monkey to your colleagues in Analysis that have to prove that they have their method validated and instruments to count bacterial growth calibrated.

Hope that helps

PR

 

[dtreacy]

Your right, I believe that this is an extremely difficult problem.
I have spent the past number of weeks contacting suppliers about calibrating these sensors and have received no definitive answer.
Therefore I am putting forward the following logic argument for not calibrating the UV sensors and run totalisers.

1) Calibration of the sensor.
Calibration of the sensor would have to deal with not only UV intensity over the expected range of the lamp(s), it would also have to deal with the UV light intensity within the narrow band around the 254 nm mark.
The calibration device would have to be able to produce an accurate 254 nm light source at a minimum of 3 intensity points (0, 30,000, 55,000 mW/cm2/s), to prove linearity and accuracy throughout the expected range of the sensor.
In addition the transmission medium (air/water/quartz) and the distance from the calibrated UV source would be critical to the calibration process.
Therefore the sensor and calibration device would both have to be able to operate throughout the expected

2) The UV intensity measurement is a single point measurement within the UV chamber. Therefore to show that it is representative of the entire chamber you would have to prove that the UV intensity is within the chamber is uniform and that the water flow through the chamber is also homogeneous (as UV intensity is measured as mW/cm2/s).
I truly believe that would be a completely impractical task.

3) Once all this is accomplished and the “calibrated” sensor is in position. The indicated UV intensity reading observed would be affected by many factors including:
· Water quality (colour, air bubbles, other factors effecting transmission)
· Quartz sleeve transmission ability (colourisation of quartz over long periods of time)
· Internal Chamber surface reflective capability
· Lamp temperatures (effects lamp output)

4) UV light provides germicidal protection for purified water loops, it is not a process step, it is a “nice to have” or safeguard.
Units are over sized so that they provide 30,000 mW/cm2/s at their end of lamp life of 60% intensity at design duty point (duty point based on flow).
UV Disinfection units are selected so that they are oversized in terms of their actual throughput (flow rate) verses their designed.
Failure of the UV disinfection unit UV intensity meter does not directly impact on quality, as it does not affect the performance of the UV lamp(s).
In addition, loss of UV disinfection can cause an increase in the systems bio burden but this is also affected by other parameters such as:
· Loop velocities (turbulence)
· Loop temperature
· Nutrients
· ID surface condition
· Loop design and dead legs
· Water turnover and usage
· Sanitisation practices

 

[MedicineEng]

My friend:
After that explanation, I don't think that any auditor will ever raise the issue of the UV calibration again...

PR