Up Your MA

Increasing the mechanical advantage of your irons set

Today, it’s not uncommon to come across fortified doors. High crime areas and high-security buildings often beef up their barrier protection against break-ins. The problem: The same barriers erected to keep out criminals can stop firefighters in their tracks.

Most truck company personnel carry a set of forcible entry tools, commonly called “irons.” Although regular irons are often not enough to access fortified doors, getting a little creative with your tools can solve the problem. By examining and applying some simple principles of leverage, we can increase the mechanical advantage (MA) of irons, making our job easier and safer.

Figure 1: A first-class lever is a lever in which the fulcrum is located in between the input effort and the output load. A force is applied (by pulling or pushing) to a section of the bar, which causes the lever to swing about the fulcrum, overcoming the resistance force on the opposite side. A Class 1 lever’s mechanical advantage (MA) is calculated by measuring the length of the lever on either side of the fulcrum. In this case, the effort arm is 5 feet and the load arm is 1 foot, creating a 5:1 MA.

Understanding MA
The effectiveness of your Halligan tool relies on the principle of leverage. Levers consist of a fulcrum (in this case, the door), the lever bar (the Halligan), the force input (pushing or pulling) and the load. To use a lever to lift a certain unit of weight with a force that could normally only lift half a unit, the distance from the fulcrum to the spot where force is applied must be twice the distance between the load and the fulcrum.

Let’s apply that to fire service tools. The average well-made Halligan bar is about 30 inches long, 6 inches of which is the fork end. The adz is also 6 inches long. To understand how much MA this tool provides, apply the principles of the Class 1 lever (Figure 1). If you’re forcing a door that opens toward you, and you drive the forked end (between the door and frame) about 3 inches deep, the doorframe is your fulcrum.

The resulting MA is calculated by measuring the length of the lever on either side of the fulcrum. The portion of the Halligan that’s in contact with the load (the door) is 3 inches. The remaining length, 27 inches, is the effort arm. This can be expressed as a 27:3 MA, or more commonly, 9:1 MA. For every 9 inches of lift (swing of the lever) with the effort arm, we rotate/move the load 1 inch. Certainly these measurements will vary from door to door and tool to tool, but this is a good average MA for a Halligan.

Compound Levers
When you insert the adz end into the doorframe (outward-swinging door) and pull back on the forked end, you’re using a lever pulling a lever, or a compound system. If you are familiar with rope pulley systems, this is just like “piggy backing” one rope pulley system on another rope pulley system.

Figure 2: In a Class 2 lever, the input effort is located at one end of the bar and the fulcrum is located at the other end of the bar, opposite to the input, with the output load at a point between these two forces.

Depending on how deep the adz penetrates, we can expect it to produce an MA (adz only) of about 2:1. Being used in this position it creates a Class 1 lever: 2 inches of the adz contacting the door, and 4 inches of the adz providing the effort arm. Of course, the adz is attached to the longer bar, and this is what we pull on, so the compound effect of the system is 9:1 MA multiplied by 2:1, for a total of 18:1 MA. This is a significant MA for this tool, and it works most of the time, especially when forcing a deadbolt lock, which requires splitting brittle materials such as wood in a doorframe. But we can do better.

In my department, we’ve been using a Denver Tool in place of the traditional flathead axe for our irons set, and it has opened up some interesting and powerful applications that increase leverage. These tools are held together and carried like a traditional Halligan and flathead ax.

Illustrated here are techniques of combining the leverage of a Halligan, and linking it together with a Denver Tool (30 inches long) to make a compound MA system.

In Figure 3, the firefighter is forcing a door that opens toward him. He has inserted the forked end between the door and frame and has linked the handle part of the Denver Tool around the adz end, catching the adz end assembly with the handle grip. This creates the lever pulling a lever. We have already concluded that just using the Halligan bar creates a 9:1 MA. If we assume the handgrip end of the Denver Tool is 3 inches, this leaves 27 inches for the effort arm (handle of the Denver Tool). This equates to a 9:1 MA. To calculate the combined MA of the compound system (Denver Tool plus adz), we multiply 9:1 x 9:1, or 81:1 MA.

Note: The calculations here are theoretical; we did not conduct actual measurements. However, doing trials on our forcible entry simulator, we felt a big difference. 81:1 seems like an amazing ratio, and it’s probable that the interface of the two tools cuts down this figure substantially. However, all we can tell you is that there is a major difference and it definitely helps.

Figure 3: Forcing an outward swinging door. Photo Steve Shupert

Try It Out
But don’t take my word for it—put it together and try it yourself.  The handle grip on the Denver Tool will allow you to use it as a cheater bar. I think you’ll be surprised at how much this small twist on a traditional tool set can make your job easier. Remember these techniques the next time you need to get through a tough door.

Steve Shupert is a lieutenant with the Miami Township (Ohio) Fire/EMS Department. A 17-year firefighter/paramedic, Shupert works on the second platoon Engine-Rescue Company 48. He is a member of the Ohio Task Force 1, and was task force leader at the World Trade Center and during Hurricane Katrina. He is also a member of the FEMA/USAR Rescue Working Group.

Figure 4: Adz pulling an outward swinging door open. Photo Steve Shupert		Figure 5: Forcing an inward swinging door. Photo Steve Shupert