Job Hazard Analysis: Rooftop unit replacement

A general example for this task. Your JHA should reflect your crew, equipment and site — review it with a competent person before work starts.

Steps, hazards and controls

1. 1. Set up roof access and fall protection

   • Fall while climbing the extension ladder to the roofMedium
     • Use the building's fixed roof hatch or stairs if available instead of a portable ladder.
     • Extend the ladder at least 3 ft above the roof edge, set it at a 4:1 angle, and tie it off at the top.
     • Keep three points of contact. Hoist tools and materials with a rope; do not carry them up the ladder.
   • Fall from the unprotected roof edge (6 ft or more)High
     • Set the work area away from the edge when possible. Use parapets 39 in. or higher or install guardrails at exposed edges near the work.
     • Set a warning line at least 6 ft from the edge, and at least 10 ft where mechanical equipment is used, with a safety monitor for anyone working outside the line.
     • Anyone working between the warning line and the edge wears a full-body harness tied to a rated anchor.
   • Fall through skylights or weak roof deckingHigh
     • Walk the roof before work and mark every skylight, hatch, and soft spot.
     • Cover skylights with secured covers or screens that hold twice the expected load and are marked COVER.
     • Never sit, step, or set tools on a skylight.

2. 2. Shut off and lock out power and gas to the old unit

   • Electric shock from the 208V–480V unit disconnect and supply wiringHigh
     • Open the rooftop disconnect and the feeding breaker in the electrical room. Put your own lock and tag on each.
     • Test your meter on a known live source, then verify zero voltage at the unit terminals phase-to-phase and phase-to-ground.
     • Discharge capacitors with an insulated tool before touching them.
   • Gas leak, fire, or explosion from the natural gas or propane lineHigh
     • Close the gas cock at the unit, lock or tag it in the off position, and cap the line right after disconnecting.
     • No smoking, torches, or grinders within 35 ft until the gas line is capped and checked with a gas detector or soap solution.
     • Keep a charged ABC fire extinguisher on the roof.

3. 3. Recover refrigerant from the old unit

   • Frostbite or eye injury from refrigerant spray at hose connectionsMedium
     • Only an EPA Section 608 certified tech connects the recovery machine.
     • Use hoses with low-loss fittings and check gaskets before connecting.
     • Wear safety glasses with a face shield and refrigerant-rated gloves when connecting or disconnecting hoses.
   • Overpressure or rupture of the recovery cylinderMedium
     • Use a DOT-rated recovery cylinder and a scale. Do not fill past 80 percent.
     • Keep the cylinder upright, secured, shaded, and away from the roof edge.
     • Keep the SDS for the refrigerant on site and review it with the crew.

4. 4. Disconnect ductwork, condensate, and prep the old unit for lifting

   • Cuts from sheet metal edges, screws, and unit panelsMedium
     • Use a cordless screw gun and tin snips; keep blades sharp and guards in place.
     • Wear cut-resistant gloves and long sleeves when handling duct and panels.
   • Strains from lifting panels, curb adapters, and partsLow
     • Use two people for anything over 50 lb, or lift it with the crane.
     • Bend your knees and keep the load close to your body.
   • Heat illness from sun and heat reflected off the roof membraneMedium
     • Schedule the lift and heavy work for early morning in hot weather.
     • Keep cool water on the roof, drink a cup every 15–20 minutes, and take rest breaks in shade.
     • Watch each other for dizziness, headache, or confusion. Give new workers time to acclimatize.

5. 5. Crane lift: remove the old unit and set the new unit on the curb

   • Struck or crushed by a swinging or dropped unitHigh
     • Use a qualified crane operator, a qualified rigger, and one designated signal person. Hold a pre-lift meeting on weights and the lift path.
     • Rig only at the manufacturer's lifting points with spreader bars. Inspect slings and shackles before the lift.
     • Barricade the ground below the lift path and keep everyone out. Never stand under the load.
     • Use tag lines to guide the unit. Stop the lift if wind gusts make the load hard to control.
   • Crane boom or load contacting overhead power linesHigh
     • Survey the setup area for power lines before the crane arrives.
     • Keep the boom, lines, and load at least 20 ft from lines up to 350 kV, or have the utility de-energize or cover them.
     • Assign a spotter to watch clearance during the whole lift.
   • Fall into the open roof curb after the old unit is removedHigh
     • Set the new unit right after removing the old one to keep the opening time short.
     • If the curb is left open, cover it with secured plywood marked COVER or put guardrails around it.
     • Anyone guiding the unit at the open curb is tied off with a harness and lanyard.

6. 6. Connect gas, power, ductwork, and condensate to the new unit

   • Electric shock if the circuit is energized while wiringHigh
     • Keep your lock and tag on the disconnect and breaker until all terminations are done and covers are on.
     • Re-verify zero voltage before you start wiring.
   • Gas leak at new pipe connectionsHigh
     • Use thread sealant rated for gas and the correct fittings; install a drip leg and shutoff per the manufacturer.
     • Leak test every joint with soap solution or a gas detector before opening the gas to the unit.
   • Skin and eye irritation from duct sealant, roof adhesives, and caulkLow
     • Read the SDS and container label before use.
     • Wear nitrile gloves and safety glasses; keep solvent-based products away from flames.

7. 7. Start up and test the new unit

   • Shock or arc flash while testing with panels openHigh
     • Only a qualified tech does live testing. Remove only the panels needed.
     • Use a CAT III or CAT IV rated meter with insulated leads, and keep one hand away from the unit when possible.
     • Wear voltage-rated gloves and safety glasses when testing energized parts.
   • Caught in condenser fans, blower belts, and pulleysMedium
     • Lock out the disconnect before adjusting belts or reaching into the blower section.
     • Keep fan guards and access panels on while the unit runs. No loose sleeves, gloves near belts, or hanging cords.
   • Carbon monoxide from a blocked flue or bad combustionMedium
     • Check that the flue and combustion air openings are clear before firing the burner.
     • Do a combustion check with an analyzer and stay upwind of the flue outlet.

8. 8. Clean up the roof and remove fall protection

   • Trips on scrap duct, screws, straps, and packagingLow
     • Pick up scrap as you go and put it in a bin or tied bundle.
     • Pick up screws and sharp pieces with a magnet sweeper.
   • Falling debris striking people below; wind blowing loose material off the roofMedium
     • Never throw material off the roof. Lower it with the crane, a hoist, or an enclosed chute to a barricaded area.
     • Weigh down or tie off packaging and sheet goods in wind.
   • Fall from the edge while taking down warning lines and guardrailsMedium
     • Take down edge protection last, after all other work is done.
     • Stay tied off while removing guardrails at the edge.