Air cylinders – differences in working pressure and valve types

What happened?

There was confusion when the wrong kind of cylinders for SCBA sets were supplied.  A vendor supplied 6.8 litre 300 bar cylinders instead of 9 litre 200 bar SCBA cylinders (as ordered).  There was no explanation.

There is only a small difference in overall size of the two types of cylinders and the size of thread for the air delivery is the same on both vent valves (v/v) heads.  Fortunately, a 300 bar filler (from a compressor) will not properly fit a 200 bar cylinder vent valve, so a 200 bar unit cannot be over-pressurised. However, a 200 bar filler and SCBA backpack will fit a 300bar cylinder vent valve.  This meant that the 6.8 litre cylinder could be filled to 200 bar (providing only 1360 litres of air rather than 2040 litres as designed).

The wrong type of SCBA cylinder v/v were also ordered, the heads come in two types – an ‘in line’ type and a ’90 deg’ type (see photo).

What were the causes?

• The supplier did not respond properly to the request for a quote (RFQ) and made assumptions about what was being requested rather than checking the RFQ carefully;
• The purchasing department did not notice or recognise that the quote provided by the supplier was not in line with the RFQ, as there was no explanation of the variation between the RFQ and the quote. At a glance, the quote looked like it related to the RFQ;
• The person originally generating the request specified the size and pressure rating of the cylinder but did not specify the type of cylinder head vent valve.

Actions taken? Lessons learned?

Ensure more thorough communication between procurement/purchasing department, vendors and persons actually generating requests.

Members may wish to refer to 

• Bailout Cylinder And Pillar Valve Compatibility Failure
• Substandard Nitrogen Quads Delivered To Shipyard
• Sustained Load Cracking In Aluminium Cylinders Manufactured From Aluminium Alloys  
• Use Of Pre-Mixed Nitrox Gases