My dear friends, I have a consultation for this large and well understood group

The NFPA 99 describes in 5.1.3.6.1 the medicinal air quality

"5.1.3.6.1 * Quality of Medical Air. Medical air shall be required to have the following characteristics: 

(1) It shall be supplied from cylinders, bulk containers, or medical air compressor sources, or it shall be reconstituted from oxygen USP and oil-free, dry nitrogen NF. (2) It shall meet the requirements of medical air USP. 

(3) It shall have no detectable liquid hydrocarbons. 

(4) It shall have less than 25 ppm gaseous hydrocarbons. 

(5) It shall have equal to less than 1 mg / m3 (6.85 × 10-7 lb / yd3) of permanent particulates sized 1 micron or larger in the air at normal atmospheric pressure"

Why is one of the most important characteristics, such as the dew point of medicinal air, not described in the medicinal air quality requirements?

If we see the quality of the Instrument Air it indicates that it must have a dew point of -40 ° F, and the code specifies alarm values for a dew point if it exceeds (-22 ° F) 

For medical air specifies alarm values when it exceeds + 2 ° C (+ 35 ° F) 

In the design of the dryers, it indicates that they must be able to deliver medical air to a dew point below 32 ° F

It is clear that the dew point of medicinal air should never exceed + 2 ° C (+ 35 ° F), however, this is the value at which the alarm is activated not the value set for medicinal air quality

Does anyone know the value established in the pharmacopeia and why does not NFPA 99 establish it?

Hi Al

I certainly think that the requirement to be met by the dryers referring to the design is also a point to consider, however, I think this is another issue

I firmly believe that the Code should clearly express in Paragraph 5.1.3.6.1 the dew point required for medical air entering the distribution line, of course, this dew point value should be lower than the value established as critical to trigger the local and master alarms 

The NFPA 99 committee should address this issue 

George Scott wrote:

USP Medical Air is silent on dew point limit (gaseous water content), at least in an older copy of their “Official Monographs” and I would guess is still the case, as it doesn’t change often. Bob, Mark or anyone else, is that still current?

USP Air does not allow liquid water and their methodology is interesting – “…no liquid is discernible on the mirror”.  Oh, test is done after an air cylinder is inverted for 5 minutes.

There are other discrepancies between NFPA 99 med air and USP med air limits and omissions.

Mr. Scott, you're absolutely right about the information you handle about the USP monograph for medicinal air

I was looking for and found that the European pharmacopoeia set the water content in medicinal air at <67 ppm, it is approximately a DP of -46 degrees C, Annex will find the comparison of both monographs and the conversion table Obviously we have a large gap in this aspect and the question I ask myself is where does this alarm value for the DP in NFPA 99 come from? What is the criterion that was used?

We see standards like the Canadian that change the minimum dew point required and prohibiting the use of refrigerated dryers

5.6.3.7.1 * Drying and purification units shall dry air to a dew point equivalent to at least -32 ° C (-25.6 ° F) at 350 kPa (50 psi). See Table D.4. Refrigerant dryers shall not be used. 

5.6.3.1.7 The medical air produced by a compressor supply system will meet the requirements of CAN / CSA-Z180.1, with the exception of a dew point equivalent to at least -32 ° C (-25.6 ° F) at 350 kPa (50 psi), as required by Clause 5.6.3.7.1.

I hope that as NFPA 99 has evolved in recent years, also see more in-depth this issue of Medicinal Air quality