SCBA fill station SCUBA

[SCBASCUBA]

There is no mechanical difference between SCBA and SCUBA compressors. The difference lies in the grade of air desired for the diving you are doing.

Grade D - Historically used in FD operations. Less than 1000 PPM CO2. Current NFPA1500 requlations now recommend Grade E for FD SCBA operations.
Grade E - Typically used in diving to depths below 50 feet Less than 500 PPM CO2(Depth might be more Im rough on the details right now) .

However, most FD SCBA compressor systems will purifiy air to Grade E standards provided Grade E is available ambiently. Typical compressor purifiers do not filter out CO2, they will add CO2 when they convert CO (carbon monoxide to carbon dioxide) Normal purfiers that are designed to maintain a constant pressure of near 1800 psi even when not in use, will allow CO2 to impinge within the purifier chambers (hold like a sponge) If air pressure were to drop in the purifier chamber, the CO will release and travel down stream to storage in one sudden burst.

Keep in mind.
Air compressors must be operating to specification. Too much oil passing rings and burning off at valves will generate high concentrations of Carbon Monoxide. Performing purifiers will convert the CO to CO2, some CO will hold within the chamber if kept pressurized.

A CO monitor is now required on SCBA compressors. As Purifiers can become saturated, fail and allow CO to pass into your storage cylinders at anytime. Air good today can fail tomorrow and you wont know it unless you have a calibrated CO monitor sampling the air as it passes the purifier.

Another question I hope I can answer for this string. Immersing cylinders in water while filling is designed to dilute the blood that will fill the room if the the cylinder explodes, while any one is near by. Filling in water was thought to cool the cylinder during the refilling cycle. The heat generated during recommpression can distort your tanks cutting down on their life (early failure during hydrostatic testing) Tests found that filling in water did not cool the air within the tank enough to have a positive effect on cylinder life or the need to top off tanks when they cool. SCBA and SCUBA cylinders should be filled using metered air flow that limits pressure rise to 1500 PSI per minute. This will avoid hot fills, distorted and stretched cylinders and the need to top off cylinders when the internal air cools.

Always fill in an approved explosion proof fill enclosure. Its your life on the line. If a cylinder were to fail during refilling chances are good someone will be seriously hurt or killed. Even a blown hose at 5000 PSI can cause major bodily damage if it were to pass too close to your skin, ear, eyes or head. Dont take a chance on your life. fill safetly.

Finally, Is there anyone in florida that can give me information on companies servicing High Pressure Breathing air? We are considering opening a sales and service center in Naples or Punta Gorda area to service FD breathing air systems. dive too. Is there a need for a professional service center in the area? Do the companies providing this service meet the needs of the customers? We are in the beginning stages of information gathering and would welcome any information you can offer.
Thank you,
Fred

 

[Steve in Seattle]

1) refer to the US Navy diving manual chapter for scuba and air.
2) refer to nstm Ch074 vol 3 for grade d air standard.
3) refer to navy safety center. Opav 1500.19d
4) refer to US Navy diving manual.

Grade D air is safe for Scuba and it will not change partial pressures of the gasses. The only difference between Grade D air and Grade E is water and oil vapor measurments.

Agreed. Compressed air is only good to depths of 6 or 7 atmospheres anyway... D is probably fine.

If SCBA was limited to 1000 ppm CO2 in the past, that's 0.1%... or 3 times the normal atmospheric level. At depth, it's only 0.006atm CO2 partial pressure at depth... about 1/3rd the threshold for symptoms to form. Considering we breath out 4% to 5% CO2, I doubt the 0.1% extra is worth worrying over. I wouldn't use it to feed a Nitrox mixer, but I doubt you'd even notice when diving on air alone... especially if SCBA's limit is now 500ppm.

That said, I'm curious what the CO limit for SCBA is... that may be a different story.

5.7.3 Cylinder Inspection and Maintenance
Cylinders should not be placed in a water bath for filling. The risk of water entering a cylinder while immersed in water and the resulting corrosion is potentially more hazardous than the risk of over-heating during filling... Water in a cylinder can create a particularly dangerous condition in cold water diving, since ice can form in the first stage or in the hose prior to the second stage valve, causing the flow of air to the diver to be interrupted.

Compressor purity is really more of an issue with Nitrox or other oxygen-rich mixing. NOAA requires less than 2 ppm hydrocarbons for their oxygen cylinders to avoid spontaneous combustion in ultra pure, high pressure oxidizer. Nitrox can be mixed without pure oxygen supplies using several methods, but higher than 40% O2 makes things more of an issue.

Some SCUBA fillers may accept 1500psi/min, but I believe the NOAA regs are for no more than 1000 psi/min to limit heating. Nitrox fills are limited to 400 psi/min while doing the air portion, but only 60 psi/min with pure O2. They also call for a top-off 30 minutes later once the gas has mixed and cooled.

Chapters 15 (nitrox) and 16 (mixed gas) in the NOAA Dive Manual cover this pretty extensively. Deep mixed-gas dives have serious concerns of gas purity (CO/CO2 being the main ones). Oxygen enriched gases have hydrocarbon concerns due to mixing... not really for dive problems.

 

[RescueDiver2407]

We have two cascades here at my FD. One is a newer model that has the tall blast cabinet to fill SCUBA bottles and is rated "E". The other is our older one and you have to use a fill whip for SCUBA bottles, and I personally REFUSE to use that one. Remember, 80% of bottle failures are at the fill station (according to PSI).

I had to check, but PSI recommends a 300-600 psi/min fill rate for all bottles.