This is Part 4 series by Senior Refrigeration Tech (and prolific writer) Jeremy Smith. Pay attention to this one folks, I know rigging and safe lifting practices may be boring to some of you, but it could very well save your back or your life.
This article is written by a technician representing his real-world experiences and his advice for best practices. You MUST understand the particular application, weight of materials and load strength of every item you use. From struts to pulleys, to anchors, ladders, ropes etc.. HVAC School is NOT giving OSHA approved safety advice. Refer to your managers, safety professionals and OSHA guidelines first and foremost. Apply any and all of these practices at your own risk with the knowledge that we are trying to help keep you from hurting (or killing) yourself.
Unistrut is your friend
The idea for a site built, customizable, gantry struck me about 4 or 5 years ago. I started by throwing a piece of unistrut over a pair of plastic folding sawhorses on the roof. The whole shebang collapsed and I had to muscle the compressor plus the weight of the strut onto the roof but I was convinced that the idea was sound. From that simple setup, I’ve experimented with using ladders, fall protection fences, and various supports I built out of unistrut. I’ve had varying degrees of success and have settled on a design that works and can be modified to suit the conditions on a job site.
Let’s start with a solid base. Looking at the “T” shaped part laying on the roof, make each piece 6’ long at a minimum and and bolt them together with a proper brace. From that solid base, install an upright and the angle bracket, again using proper fittings. The angle brace should be 2 to 4 feet long depending on the height of the upright and the height of the upright depends on what your job requirements are. I’ve used them from 30” high to one that was almost 15 feet high. Now, build a second upright, same as the first one. Remember that crossbar I said we had to just “accept” that is was there? Now it’s time to put it there for real. Using a couple 90° brackets, bolt your cross piece to the two uprights and check for level..
This may seem complicated to build and maybe it is, but a part of this is laying out the basis for some other stuff later. These pictures are from a lifting job I did. 2 15 ton Copeland scrolls up through a roof hatch that came out on a mezzanine, trolley over and lowered to the main roof level.
Note in the last picture, the chainfall is connected to a device extending out of the unistrut. That’s a trolley and it makes moving those loads once you get them up onto the roof very easy. Let’s go back to our block and Tackle example earlier. The crossbar is a piece of unistrut and, instead of connecting your pulley and rope to the bar directly, connect it to this trolley. It is now very easy to lift that load right through the roof hatch, trolley it to one side or the other and lower it onto a cart or a dolly for transport across the roof surface.
A really nice, slick setup based on this that I use very frequently is for loading and unloading these out of your truck. My van is outfitted with commercial steel shelving. If yours isn’t, you may want to just skip this part. So, cut a piece of unistrut to fit across the top of those shelves. You should really have to work to get it in and out. Once it’s wedged in there, it isn’t going anywhere. Now, take a longer piece and support it across the rungs of a ladder parked 4-5’ off the back bumper. Bolt that piece to the crossbar you just installed and, using a trolley and a ¼ ton hoist, you can easily move a compressor in and out of your truck.
Now for the cautionary stuff. Unistrut is awesome. It’s strong and relatively light, but there are limitations to its strength. Please, before you build anything I’m suggesting here, know exactly how much your load weighs and exactly how much every single piece of your lifting equipment will support. I suggest a 2:1 safety factor if at all possible, so if you’re lifting a 100-pound load, make sure that everything in your lifting system is capable of handling twice that weight. Strength information about unistrut in its various applications can be found HERE As you use this reference, pay attention to point load ratings and span figures. As span increases, point load decreases. You DO NOT want that strut failing under a load so keep your loads within the limits of your equipment. If you look closely at the crossbar I use, you’ll see that it is thicker than normal 1 ⅝” unistrut. That’s a 2 ⅛” piece and is much stronger. If you’re going to do heavier lifts, you really need a heavier crossbar like that. Be aware, the engineering specs and the catalog are very dry, boring reading but take the time to learn and know what your lifting gear will do before you have to really stress it and potentially injure yourself or someone else. Remember, the point of this is to lift and move things safely…
Genuine Unistrut P2950-EG 4 Wheel Trolley Assembly for use with P1000, P1001, P5000, P5001, P5500, P5501 and All 1-5/8″ or Taller Strut Channel
Genuine Unistrut P1325-EG 4 Hole 90 Degree Angle Connector Bracket for All 1-5/8″ Strut Channel