NFPA 921 by its own definition is a “GUIDE” which references other NFPA “STANDARDS”. NFPA 58 “Liquified Petroleum Gas Code” is a STANDARD and is referenced in 921 for PROPANE issues.

I quote 2024 ed NFPA 921 Chapter 2:

“2.1 General. The documents or portions thereof listed in this chapter are referenced within this guide and should be considered part of the recommendations of this document.”
“2.2 NFPA Publications. …
NFPA 58, Liquified Petroleum Gas Code, 2024 edition”

I further quote Chapter 10.1:
“Introduction……… NFPA 54, 49CFR Part 192, “Transportation of Natural and Other Gases by Pipeline: Minimum Safety Standards,” and NFPA 58, are generally considered to be the leading standards on this topic.”

NFPA 58 is the recognized authority in the field and the published data in the STANDARD is based upon extensive decades long testing and criteria. NFPA 58 further states: “B.1.3 Specifications of LP-Gases. Specifications of LP-Gases covered by this code are listed in GPA Standard 2140, Liquefied Petroleum Gas Specifications for Test Methods, or ASTM D 1835, Standard Specification for Liquefied Petroleum (LP) Gases.”

Here is the issue and problems that I have immediately raised to the 921 TC.

Currently NFPA 921 states:

Page 166 says, “10.2.2.2 Undiluted propane gas is heavier than air. It has a specific gravity of approximately 1.5 to 2.0, a lower explosive limit (LEL) of 2.15 percent, and an upper explosive limit (UEL) of 9.6 percent. A flammable propane-air mixture has a specific gravity of 1.01 to 1.10. Its ignition temperature is 493C to 604C (920F to 1120F).

However:

Table 26.3.2 on page 334 states:

Propane Auto-ignition Temperature: 450C-493C (842F-919F), with a specific gravity of 1.56.

Clearly the temperatures being cited are wrong, and even the 921 document doesn’t agree with itself.


The 2024 Edition of NFPA 58 “Liquified Petroleum Gas Code”, page 142, Tables B.1.2(a) and B.1.2(b) accordingly confirms the following correct information relating to LP (propane) Gas properties.

Ignition Temperature in air: 493C-549C (920F-1120F)
Specific Gravity of vapor: 1.5

It should be noted that temperature quoted in NFPA 58 of 549C DOES NOT equate to 1120F, rather it converts correctly to 1020F. So it looks like someone in the past at NFPA 58 made an calculation error and then published it, and 921 got ahold of the code, interpreted the error, and then made an error themselves in publication.

I have submitted this to several members of 921 and the NFPA Liaison in advance of their next meeting this month. I hope NFPA 921 takes this issue very seriously and corrects it (TC action or even a TIA) immediately. I will be addressing this with NFPA 58 at the next meeting.

In the meantime, I CAUTION anyone doing propane calculations to NOT RELY upon the data in the "GUIDE", follow the data and calculations in the STANDARD (NFPA 58) and double check your work BEFORE making any final determinations in your cases.

Chris Bloom - Admin
CJB Fire Consultant.