Fall, Heat, Chemical, and Electrical Hazards on a Two-Story Roof
A crew of three is installing a 120-gallon solar water heating system with two 4 ft x 8 ft flat-plate collectors on a 5:12 asphalt-shingle roof of a two-story house. Afternoon ambient is 96°F and the roof surface measures 148°F. The south edge has a 12-inch parapet, a skylight sits in the array field, and the eave is a 20-foot drop to a concrete patio. The crew has a pump-jack scaffold at the north gable but no guardrail or personal fall-arrest anchor at the south edge. A 55-gallon drum of 40% propylene glycol sits on the driveway; one worker is hand-pumping it into a 5-gallon bucket. The existing 240V AC pump circuit is being modified. The breaker is labeled “pool pump,” and the worker says he “thinks” it is off. The homeowner is watching from the patio and asks whether the glycol is toxic. The array spans two roof planes.
1. Identify the three highest-priority hazards in this setup and explain the first control you would apply to each, using the hierarchy of controls. What must happen before any further roof work?
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Stop work. The three highest-priority hazards are falls, heat illness, and unexpected electrical energy.
- Fall hazard (20 ft to concrete). The 12-inch parapet is not a guardrail. Under the hierarchy of controls, use engineering controls first: install a guardrail system with a 42-inch top rail, midrail, and toe board at the south edge, or use a personal fall-arrest system with an anchor rated at 5,000 lb per worker, a full-body harness, and a rescue plan. Administrative controls such as short duration or a warning line are not enough at this height.
- Heat illness. Provide shade, cool water, rest breaks, and acclimatization; schedule roof work for morning. PPE alone, such as hats, does not control heat stress.
- Electrical. The breaker label is not verification. Apply lockout/tagout, test the pump disconnect with a meter, and treat the circuit as energized until proven otherwise. Use GFCI protection for outdoor temporary power.
Before roof work resumes, fall protection and electrical isolation must be in place; the glycol transfer also needs correction.
2. The homeowner asks about glycol toxicity and the worker wants to hose a small spill off the driveway. Give your response and the spill-control steps.
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Propylene glycol has low oral toxicity compared with ethylene glycol, but it is not a drinkable material and should be kept away from children, pets, and storm drains. Give the homeowner the safety data sheet and explain that the system is closed and does not contact drinking water. For the small spill: put on nitrile gloves, goggles, and boots; stop the transfer; contain the spill with absorbent socks or pads; pick up the material and place it in a labeled container for proper disposal; do not hose it into the driveway or storm drain. Use a secondary-containment tray under the drum and a pump or spigot instead of an open bucket. Report any spill above the local threshold. Clean the area with detergent and water, then rinse. If the spill reaches a drain or soil, notify the authority having jurisdiction.
3. The worker proposes to skip fall protection because the parapet is 12 inches high and the job will take 'only an hour.' How do you respond and what alternative controls could make the south edge safe?
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The one-hour argument does not change the fall hazard. A 12-inch parapet is roughly knee height and does not meet guardrail geometry; it may also create a trip hazard. Duration of exposure does not eliminate the need for protection. Options: install a temporary guardrail on the south edge; use a personal fall-arrest system with a rated anchor and a rescue plan; use a mobile elevating work platform or scaffold with guardrails; or move the array work to a location that can be reached safely. If none can be implemented, stop work and involve the safety supervisor. Document the hazard assessment and the chosen control. Do not allow a worker to tie off to a skylight, vent pipe, or parapet unless an engineer confirms the anchor strength.