Speccing Apparatus for Technical Rescue Success
Aerial apparatus have come along way over the years with regard to their capabilities such as weight capacities, tip loads, turning radius, etc. Another aspect that has evolved are parts and specialized components specific to a rescue evolution that are deemed technical rescue in nature. One of these evolutions is commonly called an aerial stokes or aerial pick-off. This evolution requires rope suspended by the aerial itself in some fashion that allows for a victim and/or rescuer to access and extricate from places otherwise difficult or impossible by means of traditional ground operations. This type of evolution has been somewhat controversial depending on what part of the country, department, or culture you belong to. I have found that there appears to be two schools of thought on this.
One, it is inherently too risky as the apparatus was manufactured with relatively low tip load capacities (250-500lb) and any rope systems introduced to the aerial can increase the risk of exceeding those tip loads.
Two, departments have ordered apparatus with tip loads that can support an increased load which lends itself to the idea of suspending a victim and rescuer without exceeding the tip load.
I have found that if option two has been identified, aerial rope system ideas often start to develop as members start to look for ways to use the aerial for specific evolutions to overcome those “what if” call types. We call this being visited by the “good idea fairy” which has been known to produce some very suspect rigging to overcome a lack of specific equipment that could’ve been specified in the aerial build.
Many manufacturers will listen to your requests throughout the speccing process and point you in the direction of equipment and engineering that has been done previously by other departments. This is a good thing to listen to, as many departments have asked for specific equipment for very specific rope rescue evolutions. If the manufacturer is offering and recommending these add-ons, then chances are they have been vetted by their engineers and they work!
One example of a specialized piece of equipment, is a rope anchor crossmember made by some apparatus manufacturers for their straight frames and tiller aerials, it is removable and is specifically designed for anchoring rope systems on top of the turntable. (Fig 1) This system demands that rope be used on top of the ladder vs underneath which produces less tip load influence keeping the operation safer. The other piece of equipment that is almost a necessity if using this crossmember is a manufacturer supplied tip roller. (Fig 2) This pulley reduces friction and has a large DD ratio (Pulley, sheave ratios (Pitch Diameter of Sheave / Diameter of Rope) determining bending stress, fatigue life, and efficiency, with higher ratios (e.g. 18:1) to (40:1) reducing premature rope failure. ASME standards often require minimums (e.g., (15:1) to (18:1) for cranes, while smaller ratios increase bending fatigue and reduce lifespan. This along with introducing a force multiplier at the tip is typically why we don’t recommend rigging your own anchor and small 1.5” to 2’’ pulleys for changes of direction. These manufacturers supplied items are the “go to” way of securing proficiency and safety for a rope-based system on your aerial and MUST be specified at premanufacturing meetings. Most manufacturers will not approve or satisfy any retro work after the apparatus has been delivered.
There are ways to safely overcome these oversights if you are working off an older aerial with a tip load that your department deems safe for rope based aerial operations. Depending on the manufacturer, a tip roller type of apparatus or similar may be a bolt-on option, but you will be hard pressed to get approval for a welder to come out to create the brackets needed to hold an anchor crossmember. Creative rigging will be needed to supply a safe and efficient anchor system that does not put the apparatus or any of its components at risk. For many years departments have rigged this system off of the last rung of the bed section stating that the manufacturer has “rated” the rung at 500 lbs. This may be true, but it introduces many issues such as rope running over the aggressive anti-skid footing material applied to most aerial rungs. Recent adaptations have moved this system up to the handrails to eliminate this problem which intern has raised another. Are the handrails rated? The straightforward answer is no. However, after doing some load calculations with regard to applied force seen at the anchors given a two person NFPA Rescue Load of 600 lbs, some deem it acceptable and safe. (Fig 3) However you will probably never get a “rating” on the handrails that gives you the green light for rope rescue rigging. The ability to rig ropes over the aerial rungs and move away from the traditional paradigm of under the rungs using the aerial as a high point change of direction has made rope rescue utilizing the aerial apparatus safer with regard to tip load deviation and overload.
Another unique aerial based rope system modification is gaining popularity with the Tower Ladder community. Again, it is based on the premise of “rope over rungs” reducing any force multiplier applied during an artificial high directional operation (rigging pulleys to the bottom of the platform and running ropes through as a change of direction). Typically these apparatus have a higher tip load rating (1000lbs) and may be able to safely pull off this style of rope rescue, however by anchoring back to the apparatus itself or to the ground, the introduction of the force multiplier takes effect solely based on the interior angle of the the rope running through the change of direction (i.e the interior angle is acute at 45°, the tip load deviation force equals 185%) this means that the platform is seeing 185lbs given a 100lb load. Or in real life, a 500lb load of an attendant and victim with stokes basket and gear will equal 925lbs, almost maxing out the rated capacity of the platform. To eliminate this, anchor becketts were specced to the rear of the platform and guide pulleys on the tip of the bucket. The team can now rig all rope systems from within the platform, reducing any chance of a force multiplier as well as allowing 360° of bearing angle or lateral movement without being limited by the rope anchored to the chassis or ground. (Fig 4)
Other rescue centric prebuilt equipment and accessories should be considered in your apparatus specification based on your demographic. A couple of these accessories, receiver hitches and tow eyelets, can fulfill the need for anchors systems and winch applications. Pre-specced receivers can be called out for almost every side of the apparatus and welded at the factory with an associated rating, typically 9,000 lbs. Now, they still won’t give you an NFPA rating, however the AHJ (authority having jurisdiction) may deem it acceptable within their SOGs to use the receiver with a rope anchor style insert. Another option is to add the use of a 12 Volt Winch mounted to a hitch or commercially made hitch mount. The hitch mount with winch can stay coupled and easily removed and stored in a compartment. A very simple and economical addition if you are using this style of mounting is to have a receptacle hard wired into a place that is easily accessed by the 12 V lead from the winch. Anderson Powerpole Connectors are typical heavy duty quick link style attachments for power and can easily be mounted in a compartment out of the elements. (Fig 5)
Whether on a ladder, engine or heavy rescue, taking the time to research and investigate pre-installed components that are conducive to future rescue accessories may pay dividends down the road for quick and proficient rescue systems. These components have changed some rescue evolution designs and simplified the number of components needed as well as their set up times. All this leads to quicker evolution times, safer operations and unique standard operating procedures. Yes, these custom options will cost more at the factory, however in the grand scheme of cost per apparatus, they are a small price to pay for quicker, more efficient customer service.
Author Bio
Patrick O’Brien, Captain, is a 24-year fire service veteran and training officer with Puget Sound Fire and the South King County Fire Training Consortium overseeing ladder truck operations and technical rescue. He is an instructor with Rescue 3 International, member of the International Society of Fire Service Instructors, former Rescue Specialist with WATF-1 US&R, and co-founder of the training group KD Rescue. Patrick recently co-developed and launched the online databases and associated websites www.technicalrescuesurvey.com and www.waterrescuesurvey.com both free online reporting databases designed to help find trends in technical rescue incidents. O’Brien also developed and authored the South King County’s aerial operator program and Aerial Dynamics user manual and has been at the forefront of training prop development. With a background in small business development, technical drawing, illustration, and fabrication, O’Brien helped co-invent the SVT (Submerged Vehicle Trainer) a vehicle-in-water simulator for Swiftwater Rescue and Rescue Swimmer Operations.