Fire burns, but let’s be clear on what that means

Man is the only creature that dares to light a fire and live with it. The reason? Because he alone has learned how to put it out. – Henry Jackson Van Dyke, Jr.

Humans have learned to utilize fire’s power and enjoy its beauty and warmth, but yet we are still learning to protect ourselves from its destructive nature. In order to improve, there must be meaningful conversations and collaboration between those who study, design for, live with and fight against fire. To do so, they must all speak the same language. The English language has so many different words for concepts and ideas that are nearly identical, yet each conveys slightly different emotions, details or opinions depending on context and intent. The simple fact that each word has specific meanings allows you to (hopefully) understand what I have written here. When lives are at stake, there is no room for confusion or arguments resulting from improper use of a simple word. Knowing the exact and agreed upon definitions to certain terms used throughout the various codes and standards is also often the biggest stumbling block to understanding key concepts. The following terms are not interchangeable, and it is therefore critical that everyone understands them.

Flammable, Combustible, Non-Combustible, and Fire-Resistance

All four of these are common throughout dozens of codes and standards; the term “combustible” is used in some form almost 300 times in the IBC alone. They are also used in everyday news reports and on thousands of product labels. Once you have the real definition, you’ll be amazed at how often they are mis-used and actually lead to incorrect assumptions.

The International Building Code (IBC) and NFPA 101 actually avoid defining three of these terms in a simple sentence or paragraph because in order to be classified under one term or another, the material must be tested in a recognized manner. If the definition of what combustible meant was summarized by a highly interpretable paragraph, nobody would ever fully agree on whether something was or was not combustible. Basing a definition on whether something has passed a consistent and widely accepted set of criteria and even testing helps to reduce interpretation errors.

The first two are often used interchangeably, but should not be:

Flammable versus Combustible

Here are some official definitions. Note that I’m including the definition of noncombustible because combustible is defined as anything that cannot be called noncombustible. Yes, I know the thought, “Well, Duh…” entered your head, but it’s actually an important point.

Flammable: capable of being easily ignited and of burning quickly – Merriam-Webster.com (1)

Flammable Material: A material capable of being readily ignited from common sources of heat or at a temperature of 600°F or less. – 2015 IBC

Combustible Material: A material that, in the form in which it is used and under the conditions anticipated, will ignite and burn; a material that does not meet the definition of noncombustible or limited- combustible. – 2012 NFPA 101

Noncombustible: A material that complies with any of the following shall be considered a noncombustible material:

(1)*  A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat

(2)  A material that is reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 Degrees – 2012 NFPA 101

There are three key differences in these terms:

  • Flammable material ignites from common heat sources or at a temperature less than (or equal to) 600°F. Combustible material is ANYTHING that ignites, burns, supports combustion, etc… at any temperature or from any fire.
  • The term flammable is most commonly used to refer to fabrics, furnishings, decorations, clothing, and other such non-building related components. Combustible is more often used to describe a building material or finish that will burn.
  • Combustible materials are defined as those that would FAIL the ASTM E 136 test.

Using these definitions: All flammable materials are also combustible. Combustible materials are not always flammable. Whoa… what did he just say? Let me give an example:

A product that has been a big part of recent headlines is the metal composite material (MCM, or ACM) Reynobond PE®. It is composed of aluminum sheets (a non-combustible material) with a polyethylene foam core. Polyethylene foam ignites at a temperature of 340℃ (644℉) (2). Because the foam ignites at all it is considered combustible. The panels however would not be considered flammable as the aluminum skin does not burn (keeping flame away from the inner core under “common sources of heat”), and below 600℉; the foam core does not ignite. In this particular case, the material is NOT flammable by definition. It IS combustible. I would encourage you to read my first blog post for more discussion on the Grenfell Tower fire.

Ok, so flammable and combustible are different, but it’s just semantics right?

Noncombustible and Fire-Resistance

Let’s look at the other two terms: Noncombustible and Fire-Resistance / resistive. These unfortunately are used in similar ways, but do NOT have the same meaning.

Noncombustible: A material that complies with any of the following shall be considered a noncombustible material:

(1)*  A material that, in the form in which it is used and under the conditions anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat

(2)  A material that is reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 Degrees C

– 2012 NFPA 101

Fire-Resistance Rating: The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703. (Those tests are ASTM E 119 or ANSI/UL 263) – 2015 IBC

A material that will not ignite or burn in any way, such as steel, is considered non-combustible. Steel on its own however, does not maintain its structural strength when subjected to high heat, and therefore has a very low (if any) fire-resistance. It may sound hard to believe, but a heavy timber column (say 12 inches x 12 inches in dimension) will remain structurally sound much longer in a fire than the same size steel column.  Another common example is cementitious siding (known by the brand name HARDIEPANEL®). This product is non-combustible (3), but does little to confine a fire as it can quickly fall apart when subjected to an actual fire reaching more than 1,500℉, and therefore has little to no fire-resistance.

If you want to protect and separate the occupants of a building from a fire, you need materials and systems that are fire-resistive. They actually remain in place and hold together long enough to keep the fire away or hold the building up. There are fire-resistive systems constructed of non-combustible materials and just as many that are made with combustible materials.

Fire-resistance is not an issue of will it burn or not (combustible versus noncombustible); it is determined by how long a material or system will resist the fire and protect a building’s occupants.

It’s impossible to design, construct, or correctly maintain a building that protects its occupants if these terms are used incorrectly; besides, you’ll sound smarter using the right one.

More Information:

There are plenty of other terms related to building codes that are mis-used or mixed up that I know we’ll discuss later.

For additional information on fire-resistive properties of Aluminum Composite Materials (ACM) and the fire-resistant testing procedure ASTM E 119, please take a look at the following videos from Alucobond® and National Gypsum®.

https://youtu.be/Ku79wNywrDU

https://youtu.be/lgqDx646s-U

Footnotes:

  1. https://www.merriam-webster.com/dictionary/flammable
  2. Q & A on Fire and Fire Prevention of Rigid Polyurethane Foam, May 2009, Translation into English by JUII Fire Safety Committee from revised Japanese text, December 2011, Japan Urethane Industry Institute (JUII). http://www.urethane-jp.org/topics/doc/Q&A_on_Fire_and_Fire_Prevention_of_Rigid_Polyurethane_Foam_REV1.pdf
  3. ICC-ES Report, ESR-1844, HARDIEPANEL® (PREVAILTM, CEMPANEL®) SIDING, HARDIFLEX® SIDING AND HARDITEX® BASEBOARD https://www.jameshardie.com/JamesHardieMainSite/media/Site-Documents/TechnicalDocuments/Reports/ESR-1844.pdf