The NFPA 704 Diamond still reigns supreme as the labeling system for bulk tanks in the chemical industry and recently I posted an article about a Category 1 Flammable Gas and it’s “Degree of Hazard”. It is my professional opinion that a CAT 1 Flammable Gas is a “4” in the NFPA Flammability Hazard; however, based on texts/e-mails/phone calls I can say we are not in short supply of safety professionals who disagree with me. And almost all of those who disagree with the “black and white” view of assigning the “Degree of Hazard” to a CAT 1 Flammable Gas point to two (2) sections in NFPA 704.
(NOTE: those who are not members of SAFTENG can click on the link to access the standard for free)
In this article, I will discuss three (3) examples of how/when the NFPA 704 “Degree of Hazard” could be represented differently than when the hazardous material is stored at ambient conditions or in different locations. The three examples are:
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- Flammable Liquids stored in a refrigerated/chilled state
- Flammable Liquids processed at temperatures above their flash points and approaching their auto-ignition temp(s)
- Anhydrous Ammonia stored outside vs. inside
Here is what NFPA says about increasing or decreasing the “Degree of Hazard” for a material:
(emphasis by me)
4.2.3.1 Based on professional judgment, the hazard rating shall be permitted to be either increased or decreased to more accurately assess the likely degree of hazard that will be encountered.
4.2.3.2* It shall be anticipated that different physical forms of the material or conditions of storage and use could result in different ratings being assigned to the same material.
So as we can see, NFPA allows us some latitude to adjust our “Degree of Hazard” based on different physical forms of the material or conditions of storage and use. Here are three (3) real-life examples I can speak to where the NFPA flammability rating could be different based on the location or the conditions the materials are stored or processed.
Example #1:
Rather than store Xylene at ambient temperatures where the material could be above it’s Flash Point (FP), we “chilled” our Xylene so that the liquid was stored at around 60ºF. The FP of p-Xylene is around 80ºF, so we were storing the Xylene at a temperature that was 20º lower than it’s FP. Normally the NFPA 704 label would be a “3” in the Flammability Hazards; however, since we were storing the flammable liquid in a “chilled” state (20º below its FP) we could have taken the liberty and used a “1” in the Flammability Hazards. WE NEVER DID this, but under the standard, we could have.
PLEASE note that the PSM exemption for flammable liquids stored in atmospheric storage tanks where the liquid is kept below if BOILING POINT without the aid of refrigeration or chilling is a MUCH riskier storage practice – we chilled our xylene as we had excess capacity with our refrigeration process and chilling it saved us $ rather than using Nitrogen to blanket such a large storage capacity. Chilling to maintain temps below FP is much easier and lower risk than chilling to keep the volatile liquid below its BP.
Example #2:
We processed a combustible liquid (now called a Category 3 Flammable Liquid) at temperatures well beyond the liquid’s Flash Point (FP) of 130ºF and very close to its Auto-Ignition Temperature of 410ºF. Inside a pipe and/or a PROPERLY inerted vessel, the risks of operating above the FP and encroaching the auto-ignition temp were managed. But what would happen in the event of a Loss of Primary Containment (LOPC) event involving this material being processed in this manner? What could happen within the process if we lost our nitrogen purge? In the bulk tank in the tank farm, the NFPA 704 label showed a “Degree of Hazard” of “2” based on the ambient conditions and the hazards associated with this atmospheric storage. However, the engineering group decided that we owed the ERT and the local FD a “fair warning” of what they are dealing with in the process building with four (4) process vessels in this state. So the process vessels (dedicated to this process), as well as the door to the process building, were labeled with the CHEMICAL NAME and an NFPA Diamond with a “4” in the “Degree of Hazard” for the Flammability section. As a footnote to the NFPA 704 diamond, we added text on the “white” section of the label stating that the material is processed at a temperature which increases the hazards with the material.
Example #3:
A few years ago the International Insitute of Ammonia Refrigeration (IIAR) decided to establish different labeling requirements for Anhydrous Ammonia (NH3) based on where the container was located. Outside, where it is difficult to achieve a flammable range of NH3, the “Degree of Hazard” for the Flammability section is a “1”; inside a structure, the “Degree of Hazard” for the Flammability section is a “3” because without “adequate ventilation” it is feared that NH3 could reach its LEL of 16% or 160,000 ppm. This practice has been “codified” in ANSI/IIAR 2-2014. This “change” has caused some level of concern from the response community as they see an NFPA Diamond on the door to the “engine room” and it has a “3” in the Flammability section; it causes them concern. We have to realize that all of the SDS, Tier II Sheets, ER Guidance Software(s), Technical Manuals (including the NH3 databook), etc. all assign NH3 a “1”, so when responders see a “3” this may (should) cause some hesitation. EXCELLENT COMMUNICATIONS and planning with your in-house response team(s) and your off-site responders will help ensure everyone is on the same page. But let’s not fool ourselves, responders are being trained that NH3 is a “1”. We also have the confusion when 1-2 facility adopt this labeling practice and inform the responders and the others in the fire district do NOT adopt it – meaning that some engine room doors will have a “1” and some will have a “3”. And we have to satisfy the AHJ as well as he/she may have the final say, regardless of what IIAR-2 requires.