Associations, Fire Department, Mounting Equipment

De-mystifying Hydraulic Rescue Tool Pressures

Issue 9 and Volume 15.

Regardless of brand or model, it seems that each time a new hydraulic rescue tool hits the market with claims of pressures over 250,000 pounds of cutting force, it is met with much skepticism. How can they claim such outrageous numbers and, moreover, how can they prove it?

These are legitimate questions. The National Fire Protection Association does have tests for hydraulic rescue tools that dictate compliance with their standards, but the NFPA 1936 powered rescue tool standard does not require substantiation of specific force numbers or calculations. I have often wondered why NFPA 1936 doesn’t deal with this issue.

The controversy over hydraulic rescue tool cutter/spreader pressures is as old as the tools themselves. With the understanding that I am a firefighter and not a hydraulic engineer, I will attempt to simplify what is a very precise and complex process.

My research repeatedly brought me back to a reference manual of federal hydraulic standards, published in 1930. What I understand from the reference material and from those interviewed is that the principals and formulas contained in the hydraulic standards manual are certainly not new. There is a proven mathematical formula that provides for the calculation of cutting force and that can be, and often is, applied to hydraulic rescue tools. Where this starts to get tricky is when one begins to plug in the different variables for different tools to complete the equation.

For our purposes, let’s look at two of the many variables. The first one is the variable of push versus pull technology. Some hydraulic cutters use a pushing action to effect a cut, and others use a pulling action. The action (push or pull) of a tool is a big factor in determining force, as is the size of the components needed for each type of tool, along with the understanding that these components will often differ greatly from model to model. As a result of these differences, the values used in the equation to determine cutting force will also differ. Clear as mud, right?

Mechanical Advantage

The pull or push action of a tool will (in part) determine the type and size of components such as links required to move the cutting blades. Where the links meet or attach to the blades and the angle they create is yet another variable that will affect the calculation of cutting force. The size and dimensions of the links, and the angle created in their use add to (or detract from) the mechanical advantage of the tool.

The mechanical advantage of a tool is also a key in the overall determination of force. If you are unfamiliar with the principal of mechanical advantage, it is gained, as a simply stated example, when we use a long breaker bar to loosen a frozen nut or bolt, as opposed to using a six-inch wrench.

It is also important to note that advertised cutting forces are figured at a fixed location on a particular blade of a specific tool, and that the cutting forces are not the same throughout the blade.

Tool manufacturers’ claims of cutting forces are not based on a uniform procedure. They don’t all use the same point on cutter blades for their measurements. It is fairly safe to assume that they would use the optimum spot on their blades to obtain the best results. Please don’t misunderstand this to be a bad thing. Think of it as similar to the sweet spot on a golf club or a baseball bat.

For example, tip loading a blade (not advised) will typically produce far less force than a cut made at the base, or at the heart of the blade. Additionally, it needs to be noted that different tools reach their maximum forces at different times during a cut. Some tools reach this max near the start of a cut, and others reach it more towards the completion of a cut. It all depends upon the tool’s design and the method used to make force (energy and leverage, or mechanical advantage of that energy).

In the final analysis, I believe anyone shopping for new rescue tools should be able to obtain proof from manufacturers of their advertised forces prior to purchase. Additionally, to complement the ability to measure and calibrate optimum rescue tool pump pressures, fire departments should be able to measure cutter forces as a part of their preventive maintenance programs.

By now, we all know that new vehicle construction has made extrications more challenging and potentially dangerous. With this knowledge in mind, having to depend solely upon what tool manufacturers tell us about what their tools are capable of is a bit unnerving. This is not to suggest that tool companies are advertising anything but the absolute truth about the forces that their tools can produce. But it would be nice to have independent testing.

We can test fire hose, fire pumps, rescue tool pumps, SCBA tanks and mask seals and a myriad of other equipment. It’s a shame we can’t seem to test the forces of our hydraulic rescue tools, especially when the lives and safety of our patients, as well as our own lives and safety, hang in the balance.

In the next installment, we’ll discuss broken rescue tool cutter blades and how all blades are not created equal. Additionally, we’ll explore a reader’s submission of an extrication challenge involving a head-on MVA on a highway in Ohio. Please keep those submissions coming to [email protected]

Editor’s Note: Carl Haddon is the director of Five Star Fire Training LLC, which is sponsored in part by Volvo North America. He serves as assistant chief and fire commissioner for the North Fork Fire Department in Idaho and is a career veteran of more than 25 years in the fire and EMS services in southern California. He has also served as a fire/safety director for numerous racing organizations, including Penske Motorsports, NASCAR, USAC and Mickey Thompson Racing. He is a certified Level 2 fire instructor, an ISFSI member and teaches 5 Star Auto Extrication and NFPA 610 classes across the country.

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