Direct answer: Above roughly 10 m span, curtain self-weight, barrel deflection, wind load, and listing limits can all govern the design: expect 14–25 kg/m² of steel curtain [T], and size the motor from torque at the barrel (T = W × r), adding a 25–50% safety margin, not from nameplate horsepower.
Why self-weight governs above 10 m
A fire shutter’s steel curtain rolls onto a barrel (roller). At spans over 10 m, three self-weight effects stack up:
- Barrel deflection. The barrel sags under the curtain’s dead load. Excessive sag causes uneven coiling, slat binding, and premature guide wear. Industry practice limits barrel deflection to roughly L/400 of span [T].
- Torque demand. The operator must lift the full curtain weight wrapped at the barrel radius. Torque rises linearly with curtain weight and barrel radius.
- Governed descent energy. On fire release the curtain drops by gravity through a governor; heavier curtains carry more kinetic energy, so descent speed control and brake capacity must be re-verified at larger sizes.
Fire-rated shutters also have a hard practical ceiling: most listed assemblies top out around 12–18 m width depending on the rating (larger openings need multi-panel or horizontal-sliding solutions) [T] — always confirm against the manufacturer’s listing.
Reference parameter table (spans 10–16 m)
Assumptions for [E] values: insulated double-skin steel slats, curtain weight 20 kg/m² nominal, barrel radius r = 0.15 m, lift height = opening height, g = 9.81 m/s². Torque T = W(kg) × g × r. These are screening numbers only — manufacturer data required for final selection.
| Clear span (m) | Height (m) | Curtain area (m²) | Curtain weight @20 kg/m² [T] | Static torque @ r=0.15 m [E] | Suggested motor torque (×1.3 margin) [E] | Barrel OD typical [T] |
|---|---|---|---|---|---|---|
| 10 | 4 | 40 | 800 kg | ≈ 1,177 Nm | ≈ 1,530 Nm | 219–273 mm |
| 12 | 4.5 | 54 | 1,080 kg | ≈ 1,589 Nm | ≈ 2,066 Nm | 273–325 mm |
| 14 | 5 | 70 | 1,400 kg | ≈ 2,060 Nm | ≈ 2,678 Nm | 325–406 mm |
| 16 | 6 | 96 | 1,920 kg | ≈ 2,825 Nm | ≈ 3,672 Nm | 406 mm+ / multi-barrel |
Data levels: curtain weight and barrel OD are [T] industry nominal ranges (single-skin steel ≈ 12–16 kg/m²; insulated double-skin ≈ 18–25 kg/m²). Torque values are [E] computed with the stated formula and assumptions.
Motor torque matching method (step logic)
- Compute curtain weight: W = area (m²) × curtain mass (kg/m² from the manufacturer).
- Compute barrel torque: T = W × 9.81 × r, where r is the maximum coil radius (outer wraps), not the bare barrel — a common undersizing error.
- Apply safety factor: ×1.25–1.5 for friction, guide misalignment and aged grease.
- Check duty cycle and thermal rating: large shutters cycle slowly; verify the operator’s rated torque is continuous, not intermittent.
- Verify brake holding torque ≥ 1.25 × static torque, so the curtain cannot creep down if power fails.
- Re-verify the governor/brake for fire descent at the final curtain weight per the listing.
Scenario-based recommendations
- Warehouse firewall, 12 × 4.5 m: budget for ~1.1 t of curtain and a ~2,000 Nm class operator; confirm the barrel is engineered (deflection ≤ L/400) and the complete rolling steel assembly is listed at that size (UL lists this category under UL 10B) [S].
- Atrium opening > 16 m: use two synchronized shutters with a center mullion, or a horizontal sliding fire door — single-curtain listings rarely extend that far [T].
- Retrofit motor upgrade: do not just fit a bigger motor; re-check barrel strength, end brackets and brake capacity against actual curtain weight first.
- Frequent cycling (parking/loading): the sizing above assumes infrequent fire-shutter duty; daily cycling demands a higher duty-class operator [T].
Frequently asked questions
How heavy is a large steel fire shutter curtain?
Typical nominal range is 12–16 kg/m² for single-skin steel slats and 18–25 kg/m² for insulated double-skin slats [T]. A 12 × 4.5 m insulated curtain weighs roughly 1,000–1,350 kg.
Why does coil radius matter for motor sizing?
Torque = weight × radius. As the curtain wraps, coil radius grows, so torque demand peaks at the top of travel. Sizing to the bare barrel radius undersizes the motor by 20–40% [E].
What limits the maximum span of a fire shutter?
Listing scope and barrel deflection. Most listed single-curtain assemblies top out around 12–18 m wide [T]; barrel sag beyond ~L/400 causes binding. Larger openings need multi-panel designs.
Can I use a standard industrial door motor on a fire shutter?
Only if the operator is part of the listed fire assembly and supports fire-alarm release with governed gravity descent. A generic door motor alone does not satisfy the listing [S].
References & data provenance
| Data point | Level | Source |
|---|---|---|
| Fire-rated assembly listing framework (UL 10B/10C) and governed descent | [S] | UL — https://www.ul.com |
| Rolling steel door design conventions (barrel deflection, operator duty classes) | [S]/[T] | DASMA technical data sheets — https://www.dasma.com |
| Curtain mass 12–25 kg/m²; max listed widths 12–18 m; barrel OD ranges | [T] | Industry nominal range — manufacturer data required (e.g. https://www.cornelliron.com) |
| Torque values in parameter table | [E] | T = W × 9.81 × r; assumptions: 20 kg/m², r = 0.15 m, margin ×1.3 — manufacturer data required |
[S] = published standard/code. [T] = industry nominal range, not a measured value for any specific model. [E] = estimate from the stated formula and assumptions; final sizing must come from the shutter manufacturer’s engineering data.
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