Yes, yes, quarterly monitoring is important, and so is meeting dew point standards to prevent free water condensation (especially with regards to steel cylinders!)
However, quarterly monitoring
cannot possibly determine that during the entire period you are pumping acceptable quality gas!
There are two
separate issues here:
1. If the dew point of your gas is too high, at working pressure in your cylinder, free water can condense and this causes severe problems (e.g. corrosion in steel cylinders) which must be avoided. As pressure rises the amount of water expressed in absolute terms (mg/m^3) falls precipitously. Likewise, temperature is a significant factor, since warm gas holds more water vapor than cold gas. This is what the Draeger tubes are checking for, and what the quarterly air check does as well. In addition, if you dive (particularly open circuit) in cold water, there's a second problem in that temperatures can fall radically during expansion in the first stage. If the gas is not sufficiently dry you can get icing inside the regulator's internal mechanism which will cause a first-stage freeze with resulting malfunction. This is unlikely on a CCR due to the much lower volume of gas delivered (and thus the lower adiabatic cooling load) but happens all the time with open circuit gear.
2. However,
what I am referring to here is a way to monitor, in real-time, whether or not your purification stack is actually working. Since "online" air testing for hydrocarbon content is impractical, and quarterly monitoring does not tell you whether or not you are pumping clean gas
all the time, a proxy is helpful for determining whether or not your filter stack is expended and needs service.
The "eyeball" indicator with a 10/20/30% RH card in it, on the high pressure delivery side, is an effective means of determining the latter circumstance.
When the 10% card has "turned", you have a 10% RH in the high side of the system at delivery pressure and temperature. By the time the 20% card has started to turn,
your purification stack is no longer effectively removing moisture from the gas stream, and you are at severe risk of hydrocarbon bypass.
Since the question originally asked (and from which this thread was derived) was asking specifically about compatability of product gas with oxygen for the use of blending, moisture, while troublesome, isn't the issue under consideration.
Compressor and filter manufacturers all cite "expected service life" numbers, usually in cubic feet of gas processed. However, those ratings all require that one know the temperature of the inlet gas - and that is quite difficult to measure
accurately. Ambient temperature does not provide a reasonable guide to stack inlet temperature. Inaccuracy here leads to belief that you have working filtration when you in fact do not.
Checking quarterly only tells you that the filters are working
at the time of the check.
I note from your own quoted documents that HSE recommends:
Quote:
2 A more reliable method is to monitor the air quality on-line. One technique of monitoring on-line is to measure the moisture content.
n Filter cartridges are usually designed so that the drying element becomes saturated before there is any deterioration of the other elements. Therefore, monitoring the moisture content of the air at the filter outlet can indicate when the filter has reached the end of its life.
n On-line moisture content measurement equipment can be:
- built into the filter element; - a separate measuring device; - a simple visual indicator.
n
The provision of on-line moisture content measurement equipment will be of particular benefit where the air is for sale, as it will provide visible assurance to the user of the gas.
n
Before fitting such devices the views of the compressor and/or filter manufacturer should be sought. Which, of course, is what I recommended.
You might want to read your cites before using them, as in this case they backed up my position rather than yours!