Science, Judgment, and the Sound of Catastrophic Failure

The pros and cons of plastic vs. wood cribbing.
To the Rescue | 
I love it when firefighters of all ages, regions, and circumstances care enough about the job to engage and learn more about a topic.

In my last column, “Not All Plastic Cribbing Is Created Equal” (February 2021), we discussed some of the differences in composite cribbing on the market today. This subject stirred up an age-old debate regarding the use of wood vs. composite or plastic cribbing. This time, however, the debate brought in some “relied-on variables” that I found disturbing.

I have successfully used both wood and plastic cribbing for many years. I have seen wood cribbing fail in the field, and I have intentionally caused both plastic and wood cribbing to fail as part of a research and development project for a leading recycled plastic cribbing manufacturer. Much of my research comes from heavy industrial applications of wood and plastic cribbing that is/was used to support some of the heaviest earth-moving equipment on the planet.

The goal of this article is NOT to intentionally sway anyone toward one product or another but to state some often-overlooked facts that could possibly help you make an informed and educated decision regarding which type of cribbing would be best for your department.

By way of a public service announcement and having nothing to do with the structural integrity issues that we will discuss, please remember why the fire and EMS services did away with wooden spine boards. It was not a lack of structural integrity of wooden boards; it was the biohazard contamination concern and the inability to properly decon wood boards. Do you decon your wooden cribbing? After all, there is NO difference between the wooden spine board decon/biohazard issue and that of wooden cribbing, right? It doesn’t really matter whether a biohazard contaminated splinter in your hand comes from a wooden spine board or a wooden piece of cribbing, does it?

So as not to rehash what we discussed about plastic/composite cribbing in my last article, please review it for the details on the specifications and differences in plastic cribbing and its manufacturing.

SCIENCE

Some of the cribbing differences that came to me after my last article were regarding working load limits, point of contact load limits, and audible failure sounds. This is where I started to get worried and what prompted the title of this article. I could put you to sleep with all the science that surrounds both wooden and plastic cribbing, but I won’t. Our job as firefighters and rescuers is to “safely extricate entrapped patients in a timely manner.” Let’s look at a few basic facts about wooden cribbing.

Wood fails with the grain, and there’s no way to tell when or how it will happen. (Photos by author.)

Cut from the same tree or same limb, no two pieces of wood are alike.

Heavily used examples of 10-plus-year-old wood and plastic cribbing.

Wood cribbing pieces like this one are still in regular fire service and industrial use around the country.

Plastic cribbing offers a controlled, manufactured uniformity not found in wood cribbing.

  • No two pieces of wooden cribbing are identical, in the same way that no two limbs of the same tree are identical.
  • No wood cribbing can be accurately tagged with scientific working load limits, because no two pieces are identical. (Scientifically, we have only a general range of limits.)
  • Wood is a naturally occurring substance. It is not manufactured, only milled.
  • Wood’s tolerances are subject to load, age, climate, use, and exposure. Those tolerances change with each of the listed variables.

Even if we were to only look at the last bullet point above, it leads me to ask some serious operational and firefighter safety (departmental liability) questions:

  • Do you know what loads your current wooden cribbing has been exposed to?
  • Do you have any idea how old your wooden cribbing is?
  • How often has your cribbing been used?
  • Has your wood cribbing been exposed to temperature and weather extremes?

We all know that wood deteriorates over time. We all know that factors like weather and use speed the deterioration of wood. But do we know how quickly or slowly our wood cribbing deteriorates and how that affects the reliability of our cribbing? I don’t know about your department, but I can tell you that when we needed more cribbing for our cache, we simply added new cribbing with the existing “good” older cribbing. With that in mind, does mixing different ages of wooden cribbing change the science? I would certainly say yes, it does.

JUDGMENT

A few of the firefighters who contacted me after my previous article on cribbing seemed to be overly concerned with the science of certain cribbing and not concerned enough about the field applications. We may build crib stacks in standard ways, but no two cribbing applications are identical. Firefighting requires us to rely on our education and training. There’s an old saying, “Let the ghost of no firefighter say that his training let him down.” This is all very true and important. What we learn from firefighting textbooks, reference materials, National Fire Protection Association standards, and our peers is all good and important. That said, there comes a time where we need to rely on our own good judgment.

Another old adage states, “Just because you can, doesn’t mean you should.” In other words, just because a piece of cribbing has a scientifically calculated working load limit, or a specific point of contact limit, doesn’t mean that we should take any cribbing to the limit. The circumstances, conditions, and hopefully good judgment that we are using in deploying the cribbing will/should dictate how we load our cribbing.

I spent many years in the major motorsports industry. My Nomex® fire suit (we wore suits similar to the drivers) had a manufacturer’s certification label sewn into it basically stating (my words) that my fire suit could be engulfed in flames for 45 seconds before I sustained serious burns. That’s what the science said. Does my good judgment tell me that it’s okay for me to be in a fully involved race car for 45 seconds? NO! The same holds true for cribbing of any kind. Just because the science says that a piece of cribbing is rated for a certain contact point load or has a certain working load limit, your good judgment on its usage or application should prevail. Also, my judgment, and not the type of cribbing or the rating labels on it, determines how I would crib a vehicle in the snow on an icy highway in winter vs. how I would crib the same vehicle on a dry, solid surface in the summer.

THE SOUND OF CATASTROPHIC FAILURE

The final and probably most profound part of the recent conversations over the pros and cons of plastic vs. wood cribbing is regarding the audible sounds of wood. There is a long-standing argument between the two sides that “wood makes better cribbing because it lets you know when it’s going to fail.” In other words, it is thought that wood emits an audible warning (cracking or groaning noise) when it is going to fail. Plastic gives no such audible warning. This thought process is entirely true AND entirely false.

The typical signs that plastic cribbing is overloaded, misused, and failing are visual. When plastic cribbing fails, it starts to “flow.” Early stages of flow will look like the plastic is slowly starting to bulge or marshmallow. Wood cribbing is indeed known to give off an audible warning during catastrophic failure as the grain of the wood separates and detaches. The sound and process are virtually identical to the sounds made when using a wood splitter on firewood. Extreme point contact pressure is exerted onto the wood by the splitter until the wood breaks, making its characteristic crack, grunt, and groan noises. Wood under extreme pressure typically fails violently and instantly in the same way a dried piece of firewood reacts in a splitter.

If you take nothing else from this article, please understand one critical thing about catastrophic failure of wood cribbing and the noise (audible warning) it makes. When you hear that audible warning or the noises that I described, the wood is NOT telling you that it is GOING to fail! When the wood makes those noises, IT IS ALREADY CATASTROPHICALLY FAILING!

In the name of transparency, I have nothing against wood cribbing. I understand the financial argument for it, and I understand the practicality and ease of availability surrounding it. I am a proponent of well-made plastic cribbing from both an operational and a risk management perspective. Regardless of which cribbing you use, remember that it is an often-overlooked and undermaintained tool in your toolbox. Use good judgment in addition to the science to determine how to best use whichever type of cribbing you have at your disposal.


CARL J. HADDON is a member of the Fire Apparatus & Emergency Equipment Editorial Advisory Board and the director of Five Star Fire Training LLC, which is sponsored, in part, by Volvo North America. He served as assistant chief and fire commissioner for the North Fork (ID) Fire Department and is a career veteran of more than 25 years in the fire and EMS services in southern California. He is a certified Level 2 fire instructor and an ISFSI member and teaches Five Star Auto Extrication and NFPA 610 classes across the country.

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