Fire Watch: 30 Min Post Rule

Torch Roofing Fire Watch: 30 Min Post Rule

Most torch fires do not start while the flame is roaring. They start twenty five minutes later when everyone is on lunch break and an ember finally eats through the insulation. That is why NFPA 241 and most local codes require a full thirty minute fire watch after the last torch is extinguished. The rule sounds simple; the execution is where sites get burned.

What the Rule Actually Says

The watch must continue for a minimum of thirty minutes after the final flame is out. On combustible roofs or near storage areas the window extends to sixty minutes. The guard must remain within thirty five feet of the hot work zone and maintain visual contact with the slag path. Walk away early and you are not just non compliant, you are liable.

Hidden Ember Hot Spots

Slag can slide under parapet caps and sit on top of foam insulation. From the deck it looks cold, but the top side is still 400 degrees. Always lift the cap and shoot a thermal image. Anything over 150°F gets a water bath and a second scan five minutes later.

Check the underside of the deck from inside the building. A glowing nail tip is a ticking clock. One crew saw a nail glowing cherry red at minute 28; they soaked it and reset the clock, avoiding a midnight fire call.

Post Burn Checklist

• Sweep the deck for loose slag and remove it
• Shoot thermal images every five minutes for thirty minutes
• Log temps and photo evidence with time stamps
• Soak any reading above 150°F and re scan
• Sign the permit only after the final temp is below ambient plus 10°F

Common Shortcuts That Fail

Some roofers set a phone timer for thirty minutes and walk to the truck. The inspector wants to see continuous presence, not a timer. Stay on the roof, stay visible, stay busy scanning.

Another shortcut is the “drive by” at minute 25. The guard steps on the roof, looks around for ten seconds and leaves. Cameras will show the absence and the citation will stick. Continuous means boots on deck for the full window.

When to Extend Past Thirty

If wind speed is above 15 mph, stay an extra fifteen minutes. Wind feeds embers and can re ignite seemingly cold slag. If ambient temp is below 40°F, stay an extra ten minutes. Cold air masks heat signatures and slows the cool down curve.

Finally, if you smell any smoke or see wisping, reset the clock to zero and start the full thirty again. Your watch is not over until the roof smells like fresh air and the thermal gun shows ambient plus 10°F across the entire work area.

Need a guard who carries a thermal imager and knows the 30 minute rule by heart? Contact us and we will station an F-60 certified guard on your roof before the first torch lights.