Choosing the Right Breathing Air System!

(Admittedly LONG, but really worth the read — stick with us here!)

The Highly Variable Demand Approach to Choosing the Correct Product
By: Anthony M. Gonzalez, Owner, Eagle Compressors
(excerpts taken with permission)

What are your needs?  High pressure breathing air systems are used by fire depart­ments to refill their Self-Contained Breathing Apparatus (SCBA) and Self-Contained Underwater Breathing Apparatus (SCUBA) cylinders. It is difficult, even for the most experienced organiza­tions, to determine how many and how often they will need to refill cylinders during any given period of time. Understandably, this is or should be of significant concern to the Fire Department as the consequences of the approach taken to get to the answer will determine how successful or undesirable the equipment selection will be.

How much do you have to spend?   This response is not only universally despised but also has the very realistic potential to lead to a very short-sighted decision. Even if the question is en­tertained by the prospective customer, the amount mentioned can usually be counted on to be highly inadequate. Further­more, the response ends the discussion and little else can be learned by either party that can lead to a good decision.

The real challenge is to develop a method by which users can compare the real value of one machine size over another. For example, any of us would have difficulty in understanding the real value of a compressor with a charging rate of 21 cubic feet per minute (CFM) over one with 14 CFM charging rate. Other than the obvi­ous difference of 7 CFM, no one can see the value of one over the other without at least two other factors of performance for comparison.

One of the best ways to compare the value of machinery is to determine how fast they can do their job compared to how much they cost. Time and money are the two variable factors that would help lead the customer to a fundamentally good decision. I call this the System Calculator process. This requires obtaining critical information from the department. The steps are as follows:

 A. Data Collection
The following is information required for the System Calculator process.

1. The number of SCBA and or SCUBA gear that the depart­ment has. Do not count spare cylinders, just the apparatus that would be used if all were manned. It is important to know if the department fills for other organizations. If so, count that gear also.

2. Determine the volume of the cylinders used with the apparatus above.  Typical cylinder volumes are as shown below:

4500 PSI SCBA Cylinders

  • ½ Hour cylinders =45 cubic feet
  • ¾ Hour cylinders = 62 cubic feet
  • 1-Hour cylinders = 88 cubic feet
  • Scuba cylinders (the most popular size, 85% of the market) = 80 Cubic feet

5500 PSI SCBA Cylinders

  • ½ Hour cylinders = 45 cubic feet
  • ¾ Hour cylinders = 62 cubic feet
  • 1-Hour cylinders = 88 cubic feet
  • 75-Min. cylinder =111 cubic feet

*It can be noted in the calculation for time to fill that the SCBA working pressure is not part of the equation.  However, it is imperative to know if the customer is using or planning to fill any (5500 PSI) SCBA cylinders.  The compressor manufacturer must know about the use of the 5500 PSI SCBA as the compressor will need a different design air pressure switch that is normally used on compressors filling 2216/3000/45000 PSI cylinders.  Pressure switches on the lower pressure SCBA cylinder compressors do not normally restart until the storage pressure drops to approximately 5400 PSI, so attempting to fill 5500 PSI cylinders will not work as the compressor will not re-start to get the 5500 PSI pressure needed. 

1/2-Hour cylinders = 45 cubic feet (CF)
3/4-Hour cylinders = 62 CF
1-Hour cylinders = 88 CF

3. Determine the working pressure of the cylinders. If the cylin­ders have a working pressure of 4500 PSIG or 5500 PSIG, it will be necessary to offer a compressor with a 6000 PSIG working pressure. If the cylinders are low pressure, 2216 or 3000 PSIG, a compressor with 5000 PSIG working pressure can be selected.

However, I don’t recommend 5000 PSIG compressors in any case unless the customer has very limited funds to work with. Right or wrong, it seems the SCBA cylinder manufacturers are trying to entice all customers to go to 4500 PSIG working pres­sure as they can store the same or more volume in a lighter and smaller cylinder.

4. If the customer is seeking a stationary, electrically driven unit, determine the electrical service available in the installa­tion building. The most likely possibilities are as follows:

Single phase, 208/230 volts
Three phase, 230 volts
Three phase, 460 volts

Be aware that if the installation building has only single phase available, the largest compressor that can run on this current is 10 horsepower.

B. Target Volume

In order to compare the value of one compressor size over another, a baseline factor is necessary. The best way to do this is by developing a target volume that is calculated as follows: Target Volume = # of SCBA Cylinders x Volume of Cylinders

This can be calculated from the number of cylinders and their volume obtained from the customer in item #2 above.

C. Layout of the Options

Now armed with the data collected, generate a spreadsheet that will demonstrate the value of each com­pressor size in terms of speed to fill and cost. For an example of what this looks like, let’s assume the following data was obtained from the customer:

Target Volume Calculation:

Number of and Volume of Cylinders:

40) 4500 PSIG, 1/2-hour (45.0 CF) cylinders
15) 4500 PSIG, 1-hour (88 CF) cylinders (for Hazmat team)
Target Volume = 40 x 45 x 88 = 3,120 CF

Compressor CFM Time to Fill* $
14 3.7 hours $45,000.00
21 2.5 hours $51,000.00
24 2.1 hours $53,000.00

*Time to Fill = Target Volume/Compressor CFM/60

It is human nature to compare two related factors. When presented with a table as the one shown above, the natural focus is on the time versus cost columns. NOW, there can be an intelligent assessment about the value of each compressor size.

So, this begs the question once again:  what are your needs?

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