This past week I was having a conversation with my friend and fine PSM professional Brian Chapin @ RCE and our discussion turned to diffuser tanks. Having been involved in several design and install projects over the past several years, getting to know a little something about diffuser tanks comes with the territory. But one of my biggest battles has been the use of “farm tanks” (i.e. plastic tanks) as diffuser tanks. We laughed for a moment and Brian in his usual fashion brought it all home with the question… what RAGAGEP are you using for your diffuser tank(s)?
Over the last couple of years, I have fought, to no avail in some projects, trying to get clients to use truly engineered diffuser tanks. No offense to the Tractor Supply retail chain, but I swear they have sold some plastic tanks that have found their way into PSM/RMP covered processes as a “diffuser tank”. And I am not joking! As Brian and I began discussing these concerns he mentioned that there may be a RAGAGEP I could use and in some states it would be “code” to us NFPA 1. NFPA 1, 53.2.2.3 Design of Ammonia Diffusion Systems very closely follows the 2015 International Fire Code until we get to:
53.2.2.3.5 The tank shall be substantially constructed of not less than 1/8 in. (2.51 mm) (10 gauge) steel.
Yes, there we have a requirement that a diffuser tank be constructed of not less than 1/8 in. (2.51 mm) (10 gauge) steel; NOT plastic. So as we know, process safety is all about adopting our chosen RAGAGEPs so some facilities may NOT choose to use NFPA 1 and rather go with the IFC, IIAR, or ASHRAE; which all have sizing criteria and some design criteria BUT ONLY NFPA 1 has a materials of construction criteria.
But some businesses may NOT have a choice, as some states have officially adopted NFPA 1 as their state fire code. Most states adopt the IFC, but some states (19 to date) have adopted NFPA 1. As I said earlier, there is NOT much difference between the IFC and NFPA 1, but for ammonia refrigeration systems built in the past couple of years that require a diffuser tank, NFPA 1 may throw a curve ball if a plastic tank was used AND your facility is located in any of the following states:
- Connecticut (2003)
- Delaware (2015)
- Florida (2012)
- Hawaii (2006)
- Kentucky (2012)
- Louisiana (2012)
- Maine (2006)
- Maryland (2015)
- Massachusetts (2012)
- Michigan (2006)
- Nebraska (2003)
- New Hampshire (2009)
- Rhode Island (2012)
- Mississippi (2012)
- Tennessee (2003)
- Texas (2012)
- Vermont (2012)
- West Virginia (2012)
- Wisconsin (2012)
And yes I went all the way back to NFPA 1, 2003 edition and it was required in that addition as well. What this means is that for those states that adopted NFPA 1, 2003 a steel diffuser tank was required starting in 2003.
So there we have it, use plastic tanks in your diffuser system at your own risks. NFPA saw fit to require the diffuser tank be substantially constructed of not less than 1/8 in. (2.51 mm) (10 gauge) steel and that should be advice well taken.