We have had air monitoring carried out in our factory by an occupational hygienist. The method used was drawing air samples through a gastic pump. The factory is a fabrication facility carrying out welding and oxy-propane cutting of heavy steel plate. The results were alarming, in that the oxygen readings were 23% in the welding areas and 25% in the profiling areas. There is no ventilation in the factory, nor is there any fume extraction.
The Works Director refuses to accept the results and has been taking his own readings using a personal gas monitor, which does not show the same concentration of oxygen, clearly because it is not the correct instrument to measure the oxygen levels.
What is the technical explanation for using a gastic pump, and why will the personal gas monitor give inaccurate readings?

It is of some concern that you appear to have an oxygen enriched atmosphere.

SOunds like you need to check your oxygen bottles and pipes for leaks

Is the higher concentration in a very localised / confined area?

In a typical fabrication shop, with normal air movement, doors opening etc - in my experience its difficult to get an oxygen enriched atmosphere

I would check the calibration/accuracy of the instruments used so far.

Investigate as you are increasing your fire risk with an oxygen enriched atmosphere.

Oils and greases in the area are not adviseable

http://www.bcga.co.uk/pr.../publications/SL0205.pdf

http://www.hse.gov.uk/pubns/hse8.pdf

I assume the Gastek pump is drawing the air through an indicating tube that needs to be read off to provide the answer? If this is so, they are inherently subjective and therefore not a precision test. Also the tubes are one-off and cannnot be individually calibrated in the workplace.

The personal monitor on the other hand can easily be calibrated using outside fresh air, taken into the workplace where many readings can be taken and then back into the fresh air for re-check. For my money, the personal monitor is the way to go.

That doesn't preclude the possible need for LEV or other controls against fume exposure!

what is oxy-propane cutting????

do you mean oxy-acetelyne?

Looking at your recent posts it looks like you have your work cut out there!

I don't see why a decent, calibrated personal gas monitor would give inaccurate results but it would need to be sampling at the same area and time as the other system to produce comparable results. If your manager is just walking through the workshop he isn't really getting a representative sample. If the monitor has datalogging you could place it in a work area for a full shift to get an idea of what you are dealing with followed by spot samples at "problem areas".

The concentration levels do appear to be very high so don't know if there are enclosed or confined areas in your workshop where there are localised hazard areas and these would be the focus in terms of designing this out.

Another thing is that this (suspected) hazard is transportable as work clothes can become "saturated" with 02 and remain flammable for a considerable period of time after leaving the problem area. Hanging them in fresh air does the trick.

Should the methodology, rational and conclusions not be part of the Occ Hygienists report? Just wondering why management can dismiss the findings as they obviously cannot peer review it.

Good luck.

Davie

But a personal monitor left in place and monitored for the "5 - 10 minutes" will effectively take a representative sample and will also indicate peaks and troughs in concentration. If your occ hygenist is finding an average of 25% O2, I would be very worried about the higher concentrations that would contribute to that average.

The other advantage of an electronic monitor is that the instantaneous readout will help identify sources of the O2 by showing localised high readings.

There is one more thing you can do and that is to calculate how much volume of O2 from the cylinder would be needed to give the suspected enrichment in your unventilated room - I would guess it would be one hell of a lot.

Thanks for all the responses guys, but this thread seems to have gone off topic. There is a guidance issued by the HSE (MDHS 70), and the Gastec pump is one of the methods used to measure airbrne gases and vapours. The personal gas monitor, although technically able to measure oxygen content, is not a recognised method and the readings that it produced would not be a reliable foundation for a risk assessment.
The oxygen measurement was only part of the occ. hygienist's remit as we measured ozone, weld fumes, respiritable particles etc.. I was asking so that I could put a valid argument to my Works Director over his choice of measuring equipment.
Incidentally, the factory has an internal volume of 156,000 cubic metres. Thanks again for all the comments and help.

Ians
You seemed to miss the point of my original post. We have already accepted that there is a need for LEV to remove the welding fumes in the factory. This wasn't the question that I was asking. I was asking;
'What is the technical explanation for using a gastic pump, and why will the personal gas monitor give inaccurate readings?'.
Lets just leave it there please, I havent insulted anyone deliberately, and if anyone is, then please accept my apologies.
Subject closed for me now.