Fire Resistance Ratings of Fiberglass Cable Trays vs Metal Alternatives

Fire resistance rating in cable tray selection is the documented performance of a tray material under a defined fire test standard — how readily it ignites, how fast flame spreads across its surface, how much smoke it releases, and whether it keeps supporting cables while the fire is burning.

Fiberglass and metal achieve that rating in opposite ways. Glass-reinforced plastic trays typically carry an ASTM E84 Class A result (flame spread index ≤ 25, smoke developed index ≤ 450) and pass UL 94 V-0 with self-extinguishing behavior in under 10 seconds. Steel trays hold no flame-spread rating at all, because they add no fuel — but steel conducts heat at roughly 50 W/m·K and loses about half its yield strength by 500 °C before melting at 1,370–1,540 °C. Aluminum also adds no fuel, yet melts near 660 °C. So the real question is not which material is fireproof — nothing is — but which failure mode your plant can live with: a tray that feeds the fire, or a tray that moves heat into your cables.

Key Takeaways

• FRP trays are rated for flame spread, smoke, and self-extinguishing behavior; metal trays are rated for non-combustibility and structural survival.
• ASTM E84 Class A (FSI ≤ 25, SDI ≤ 450) is achievable in FRP with halogen-free, hydrated-alumina-filled resin systems.
• Steel's real weakness in a fire is heat transfer — it radiates and conducts heat back into cable insulation.
• Aluminum fails earliest on melting point (~660 °C), even though it contributes no fuel load.
• Coating choice (hot-dip galvanizing to ASTM A123, 65–85 µm) decides how long a metal tray survives chemically, not thermally.

How Fire Performance Is Actually Measured

There is no single "fire resistance rating." Buyers comparing trays are usually looking at four or five different tests at once.

Standard	What it measures	Typical FRP result	Typical steel result
ASTM E84 / UL 723	Surface flame spread & smoke	Class A, FSI ≤ 25, SDI ≤ 450	Non-rated (no fuel load)
UL 94 vertical burn	Self-extinguishing behavior	V-0, extinguish < 10 s	Not applicable
IEC 60332-3-24 / ASTM D635	Vertical tray flame propagation	Limited propagation; burn rate typically < 40 mm/min	No propagation
ASTM E136	Non-combustibility at 750 °C	Not applicable (organic resin)	Passes
EN 13501-1	European reaction-to-fire class	Usually B2 or C-s2,d0; better with additives	A1
NEMA FG-1 / VE-1	Tray construction and load class	Defines FRP tray build	Defines metal tray build

A pattern appears fast: metal wins the "does not burn" column, FRP competes in the "how does it burn" column. Those are different questions, and specifications that blur them cause most of the arguments on project reviews.

What Fiberglass Cable Trays Deliver Under Fire

FRP tray performance is a resin problem, not a glass problem. Glass fiber doesn't burn; the thermosetting matrix decides the fire signature.

• Resin chemistry: vinyl ester and isophthalic polyester are the workhorses. With hydrated alumina or phosphorus-based additives they reach ASTM E84 Class A and UL 94 V-0.
• Decomposition onset: the resin breaks down around 200–300 °C. It chars, forms an insulating carbon layer, and self-extinguishes once the ignition source is removed.
• Smoke and toxicity: halogen-free formulations cut acid-gas release — significant in cable tunnels, where HCl from PVC-jacketed cables is often the larger hazard.
• Structural retention: an FRP tray holds shape through a flash fire, but above roughly 250 °C its modulus drops quickly. It is not a fire barrier and shouldn't be specified as one.
• Thermal conductivity: about 0.3 W/m·K, roughly 1/150th that of steel. Heat does not travel along the tray into adjacent bundles.
• Fuel contribution: FRP runs 1.8–2.0 g/cm³ against 7.85 g/cm³ for steel, so the combustible mass in a tray run is small and predictable.

What Metal Trays Do When the Fire Starts

Metal has one advantage no polymer matches: it adds no fuel. It also has one problem no coating solves.

Hot-dip galvanized steel

• Melts at 1,370–1,540 °C; roughly half its yield strength is gone by 500 °C.
• Zinc coating to ASTM A123 typically runs 65–85 µm; in chloride service, coating consumption of a few micrometres per year sets the re-inspection cycle.
• High conductivity means a fire below the tray shows up as hotter cables above it.

Stainless steel (304/316L)

• Same thermal profile as carbon steel, far better corrosion resistance.
• Cost premium of 3–5× galvanized in most markets.
• Often selected because a specification rules FRP out, not because performance demands it.

Aluminum

• Melting point around 660 °C — first to fail structurally in a hydrocarbon fire.
• Excellent strength-to-weight ratio, non-magnetic, no fuel load.
• EN 13501-1 class A1, but A1 says nothing about how long the tray stays on its brackets.

Side-by-Side Comparison

Factor	FRP / GFRP	Galvanized steel	Stainless steel	Aluminum
Reaction to fire	ASTM E84 Class A; UL 94 V-0	Non-combustible	Non-combustible	Non-combustible
Flame spread index	≤ 25	0	0	0
Decomposition / melting	200–300 °C (char)	1,370–1,540 °C	1,370–1,450 °C	~660 °C
Thermal conductivity	~0.3 W/m·K	~50 W/m·K	~16 W/m·K	~205 W/m·K
Density	1.8–2.0 g/cm³	7.85 g/cm³	7.9–8.0 g/cm³	2.7 g/cm³
Corrosion resistance	Excellent	Moderate, coating-dependent	Very good	Good, galvanic risk
Typical design life	25–30 years	10–20 years	25+ years	15–25 years
Relative material cost	1.5–2.5× galvanized	Baseline	3–5× galvanized	2–3× galvanized

FRP wins on chemistry and weight. Metal wins on temperature survival. Nobody wins both.

Where the Rating Gap Changes Your Design

Three consequences show up in almost every project review.

• Heat transfer, not ignition. In a cable tunnel the dominant failure is cables overheating because the tray above them got hot. FRP's low conductivity breaks that path.
• Smoke is the rating nobody reads. ASTM E84's smoke developed index is where FRP specifications are won or lost. Halogen-free systems hold SDI under 450; cheap resins don't.
• Reaction-to-fire is not fire resistance. If the spec calls for a 60- or 90-minute fire-rated system, the protection comes from a coating, board, or enclosure — not the tray.

Matching Tray Material to Plant Environment

• Chemical and chlor-alkali plants: acid and chloride atmospheres destroy galvanizing. FRP has no electrochemical cell to corrode.
• Wastewater and desalination: humid, saline, frequently outdoors. FRP needs no recoating, and 25–30 years matches the civil works.
• Petrochemical and refinery: steel usually wins, because hydrocarbon fire exposure is a design case and the spec will demand non-combustibility.
• Offshore and marine: weight is money. FRP at ~25% of steel weight cuts structural steel in the support system.
• Data centres and dry indoor plant: galvanized steel is the economical default; the fire load comes from cables, not trays.

Building the Complete Corrosion-Resistant System

Cable trays rarely stand alone. The specification that selects FRP trays for a chemical plant normally covers the vessels, pipework, and process equipment inside the same battery limit — and sourcing them from one laminate family keeps resin chemistry and corrosion allowances consistent.

On tank farm projects, tray runs feeding pump stations and loading arms are commonly specified alongside a GRP/FRP Storage Tank built from the same corrosion-resistant laminate family.

Buried service raises different questions. A Fiberglass Underground Storage Tank has to resist soil load, groundwater, and sometimes buoyancy, so the design conversation shifts from reaction-to-fire to structural and chemical performance — the same shift that applies when you bury a cable duct instead of running a tray overhead.

Above ground, vertical duty dominates. A GRP/FRP Vertical Storage Tank is typically specified for acid, brine, and process water service where the vessel and the tray routing share one atmospheric corrosion challenge. Hebei Yongchang Composite Material Technology Co., Ltd. produces these FRP products in Hengshui, Hebei, on six fully automatic microcomputer-controlled filament winding lines across a 50,000 m² facility, supplying chemical, light industry, pharmaceutical, metallurgy, and brewing applications.

FAQ

Does a fiberglass cable tray have a fire rating?

Yes — a reaction-to-fire rating rather than a structural fire-resistance rating. FRP trays are typically tested to ASTM E84 (Class A), UL 94 (V-0), and IEC 60332-3-24. They self-extinguish but are not designed to carry load through a 60- or 90-minute fire.

Is a steel cable tray fireproof?

No. Steel passes ASTM E136 at 750 °C and adds no fuel, but it conducts heat and loses strength above roughly 500 °C.

Which tray releases less smoke?

Steel and aluminum release essentially none by themselves. Among polymer trays, halogen-free FRP with an SDI below 450 is the better choice — though PVC-jacketed cables are usually the larger smoke source in a tunnel.

What temperature do FRP trays fail at?

Resin decomposition begins around 200–300 °C. The tray chars and loses stiffness above that, and may self-extinguish rather than keep burning.

Is FRP cheaper than galvanized steel?

Not on first cost. FRP runs 1.5–2.5× the price of hot-dip galvanized steel; payback comes from 25–30 years of service without recoating in corrosive conditions.

Which One Should You Specify?

Choose FRP when the environment is chemically aggressive, weight matters, and the fire case is an ignition-and-spread scenario rather than a long hydrocarbon burn. Choose steel when the design fire is severe, the specification demands non-combustibility, or the atmosphere is mild enough that galvanizing survives its planned life. Choose aluminum when weight dominates and fire exposure is short-duration.

On most chemical, wastewater, and marine projects the answer lands on FRP trays paired with compatible FRP vessels and pipework — one laminate family, one corrosion allowance, one inspection cycle.

Fiberglass Cable Tray vs Steel: Which Is Better for Offshore Platforms?

A fiberglass cable tray is a pultruded glass-reinforced polymer (GRP/FRP) cable support system, and on offshore platforms it is specified instead of galvanized or stainless steel when chloride corrosion, topside weight and maintenance access decide the material call.

For most open-deck, riser and module cable routes, the honest answer is fiberglass. GRP trays do not rust, weigh roughly a quarter of an equivalent steel tray, and hold their mechanical properties for 20–25 years in a marine atmosphere. Steel keeps the job in high-temperature process areas, jet-fire-rated zones, and anywhere heavy short-span loading or immediate local repair outweighs corrosion risk.

The short version:

• Weather deck, riser and module routes → fiberglass.
• Fire-rated escape routes, hot process areas (>120 °C), jet-fire zones → steel, or a GRP system with tested fire-rated enclosure.
• Mixed environment on one platform → hybrid route plan, material selected zone by zone.

Key Takeaways

• Fiberglass is the default material for ISO 12944 C5-M marine atmospheres; steel needs galvanizing plus recurring recoating, or a higher alloy grade.
• Pultruded GRP runs near 1,800 kg/m³ against roughly 7,850 kg/m³ for carbon steel — a three-to-four-fold weight saving per metre of route.
• Steel stays non-combustible above 400 °C; standard fire-retardant GRP handles continuous service around 120 °C.
• Over a 20-year field life, lifecycle cost usually flips the decision that purchase price alone would not.
• Every choice still has to be checked against the IEC 61537 load class and the platform's earthing design.

Why Offshore Decks Punish Steel Cable Trays

A platform is a corrosion test rig with people living on it. Salt-laden air, 80–100% relative humidity, deluge washdown, sour gas traces and UV radiation attack metal supports from every direction at once.

• Atmosphere: ISO 12944-2 puts offshore and coastal installations in category C5-M, "very high corrosivity, marine."
• Salt spray: Hot-dip galvanized steel at 85 µm typically shows first red rust between 720 and 1,000 hours in an ASTM B117 neutral salt spray test.
• Stainless is not a free pass: 316L resists pitting in chlorides up to a point, but crevice corrosion accelerates above roughly 60 °C in concentrated brine.
• Access: Every maintenance hour offshore is expensive. A tray that needs recoating every few years is a schedule problem, not just a materials problem.
• Weight: Structural steel topside costs real money per kilogram. Cutting support steel also cuts deck load and, on floating units, ballast demand.

Fiberglass vs Steel Cable Tray: Side-by-Side Comparison

Factor	Pultruded GRP/FRP	Hot-dip galvanized steel	Stainless steel 316L
Density	~1,800 kg/m³	~7,850 kg/m³	~8,000 kg/m³
Tray mass per metre (300 mm ladder)	roughly 1.5–3 kg/m	roughly 4–7 kg/m	roughly 4–7 kg/m
Corrosion in C5-M	Not attacked by chloride	5–10 years to first red rust at 85 µm zinc	Pitting and crevice risk in warm brine
Expected service life offshore	20–25 years	7–12 years with recoating	15–25 years, grade dependent
Fire behaviour	ASTM E84 Class A; LOI ≥ 28% (ASTM D2863)	Non-combustible	Non-combustible
Max continuous temperature	~120 °C (vinyl ester resin)	400 °C+	500 °C+
Electrical continuity	Requires separate bonding conductor	Inherent	Inherent
Purchase price	~1.5–2.5× galvanized	Baseline	~3–5× galvanized
Maintenance routine	Washdown and visual inspection	Recoat every 3–5 years	Passivation and inspection

The table makes the trade-off visible: you pay more per metre and accept a lower temperature ceiling, and in return you delete the corrosion maintenance cycle.

Corrosion Performance: Where Steel Loses Ground

ISO 12944-5 treats an 85 µm zinc coating as a medium-durability system, which means first maintenance in roughly five to seven years in C5-M conditions. A duplex system — galvanizing plus a suitable topcoat selected under a standard such as NORSOK M-501 — stretches that to 20 years, but it is a coating system with an inspection regime attached, not a material property.

GRP works differently. The resin matrix is chemically inert to chlorides, so there is no sacrificial layer to consume. Two details matter in practice:

• Resin choice: Isophthalic polyester covers general marine exposure. Vinyl ester is the specification where acid splash, solvent or produced-water contact is possible.
• Surface protection: A synthetic surface veil or polyester surfacing mat keeps glass fibres away from the surface, which blocks wicking and UV degradation.

For verification, buyers should ask for mechanical and hardness testing rather than a datasheet claim: tensile strength to ASTM D638 (typical pultruded GRP values fall in the 200–400 MPa range along the fibre axis), flexural properties to ASTM D790, and Barcol hardness to ASTM D2583 as a cure check on delivered panels.

Weight and Structural Load on Topside Structures

Cutting mass is not a side benefit offshore — it propagates. Lighter trays mean wider support spacing, fewer brackets welded to primary steel, less hot work, and lower deck loading.

• A pultruded GRP profile has a density near 1,800 kg/m³ versus 7,850 kg/m³ for carbon steel, so a GRP tray typically weighs 25–35% of its steel equivalent.
• The trade-off sits in stiffness, not strength. Pultruded GRP shows a flexural modulus in the 15–20 GPa range against about 200 GPa for steel, so deflection usually governs the span table rather than stress.
• That is why GRP ladder tray is commonly specified with shorter spans for heavy power cable fills and longer spans for instrument cable bundles. Always build the route from the manufacturer's load-versus-deflection curve, with the project's deflection limit (often L/200) applied.

Fire Performance and Regulatory Acceptance

This is where steel advocates push back hardest, and they are not wrong to. Steel cannot burn. GRP can, unless the resin system is formulated not to sustain combustion.

• Fire-retardant GRP grades are tested to ASTM E84 and reach Class A ratings, meaning a flame spread index of 25 or below.
• Limiting oxygen index testing to ASTM D2863 commonly returns values of 28% or higher for offshore-grade formulations, above the ~21% oxygen in air.
• IEC 61537 is the governing standard for cable tray systems and covers classification, load testing and material performance; project specifications often layer owner and classification-society requirements (DNV, ABS, Lloyd's Register) on top.
• In fire-rated boundaries and escape routes, the deciding element is usually the enclosure or the fire-rated system as a whole, not the tray material. The cable itself often carries more combustible load than the tray beneath it.

Specify fire performance as a tested system result, not as a resin description.

Earthing, Bonding and EMI: The Hidden Specification Item

GRP is an electrical insulator, and that changes the design, not the viability.

• A separate earth continuity conductor — typically tinned copper sized by the project, often 6 mm² and upward — must run the full route and be bonded at every joint and at both ends.
• Lightning protection design follows IEC 62305 principles, and hazardous-area installations under IEC 60079 require documented bonding continuity as part of the inspection regime.
• Steel trays give continuity for free, but a steel tray is not automatically a compliant earthing conductor either — the same bonding discipline applies.

Budget for the conductor and the bonding hardware when you compare costs, because it is a real line item on a GRP route.

Service Life, Maintenance and Lifecycle Cost

Purchase price is the number everyone quotes and the wrong one to decide on. On a 20-year field life, three cost lines separate the materials:

• Capital: GRP trays typically land at 1.5–2.5× the price of a galvanized steel tray of the same width. Stainless can run 3–5×.
• Recurring maintenance: Galvanized steel in C5-M needs recoating on a roughly 3–5 year cycle, with offshore access and scaffolding costs often exceeding the coating material itself.
• Replacement: A galvanized route may be replaced once or twice in a 20-year life. A correctly specified GRP route is normally inspected, not replaced.

On an indicative 20-year cost index where a galvanized steel route is set at 100, a GRP route commonly lands between 60 and 90 once recoating, access, and one partial replacement are included. The gap widens in the splash zone and in areas with chemical spill risk.

Where Steel Still Wins

Fiberglass is not a universal answer, and pretending otherwise damages your credibility with the structural engineer.

• High temperature: Above roughly 120 °C continuous, standard GRP resins lose mechanical performance. Steel does not care.
• Jet fire and hydrocarbon fire scenarios: Steel remains the conservative choice unless a tested fire-protected GRP system is specifically approved for the zone.
• Heavy short-span loading: Very dense power cable fills or high-impact locations from dropped objects favour steel.
• Field modification: Steel can be cut, welded and re-galvanized or coated on site by a competent crew. GRP is machined and re-sealed, and joints rely on correct bolting and sealing practice.
• Static dissipation: Where a conductive path is a hard requirement, steel needs no additional engineering.

Specifying a GRP Cable Tray for Offshore Duty

Work through this sequence before releasing an inquiry, and the material debate usually resolves itself:

• Assign an ISO 12944-2 corrosivity category to each cable route, zone by zone.
• Select the load class per IEC 61537 (or NEMA VE 1 for US-spec projects) using total cable weight plus a safety factor.
• Set the deflection limit — L/200 is common — and take spans from the manufacturer's test data.
• Fix the resin: isophthalic polyester for general marine, vinyl ester for chemical exposure, fire-retardant grade with LOI ≥ 28% where required.
• Confirm UV stabilisation and a surface veil on all exposed faces.
• Detail the earth continuity conductor, bonding jumpers and support spacing.
• Require test certificates: ASTM D638 tensile, ASTM D790 flexural, ASTM D2583 Barcol hardness, ASTM E84 fire data.

Where the material sits next to process equipment, the same reasoning applies across the whole package. A route plan that already uses GRP for cable support often makes sense paired with a GRP/FRP Storage Tank for brine, inhibited acid or produced water on the same deck, since both face identical chloride exposure and both benefit from one corrosion strategy rather than two.

The logic extends to the shore base, too. A Fiberglass Underground Storage Tank buried at the supply yard or used for below-deck drainage duties faces wet, saline soil that eats coated steel in a decade, and it carries the same resin chemistry as the tray above it. Manufacturers such as Hebei Yongchang Composite Material Technology Co., Ltd., working from a 50,000 m² facility in Hengshui, Hebei with six fully automatic microcomputer-controlled filament winding lines, produce pipe, fittings, flanges, cable tray and tanks from a common GRP family — which simplifies spares and inspection paperwork offshore.

Footprint matters topside as well, where every square metre competes for space. A GRP/FRP Vertical Storage Tank occupies a small deck patch while holding dosing chemicals or wash water, and it can be specified in the same vinyl ester chemistry as the cable tray, so one material approval covers several items in the same hazardous area.

FAQ

Is fiberglass cable tray fire rated for offshore use?

Fire-retardant GRP grades tested to ASTM E84 achieve Class A ratings and limiting oxygen index values of 28% or higher. Whether that satisfies the zone depends on the project: escape routes and fire-rated boundaries usually require a tested fire-rated system, which may mean steel or a protected GRP assembly.

How much lighter is GRP than steel?

Pultruded GRP density is around 1,800 kg/m³ against roughly 7,850 kg/m³ for carbon steel. In practical tray terms, a 300 mm ladder tray drops from about 4–7 kg/m to about 1.5–3 kg/m, which reduces support steel and installation crane time.

Do fiberglass trays need an earth continuity conductor?

Yes. GRP is non-conductive, so a separate tinned copper conductor must run the route with bonding at every joint and at both ends. Size it to the project's fault-current and IEC 61537 requirements.

**How long does GRP cable tray last on