ACP Fire Rating Guide & ASTM Calculator

Section 01

ACP Core Classifications Explained

Aluminium Composite Panels (ACP) are three-layer assemblies: two thin aluminium skins bonded to a core. The core is the fire-defining component. Its chemical composition determines whether the panel is a passive fire barrier or an active fire accelerant. Four primary classifications exist under EN 13501-1 (Europe) and ASTM E84 (USA):

A1

Non-Combustible · Highest Grade

Core is almost entirely inorganic mineral — typically aluminium hydroxide (ATH) and magnesite. Will not ignite, sustain flame, or generate smoke under any fire condition. Zero fuel contribution to a fire event. The benchmark standard for high-rise and public buildings globally.

Organic <1%

A2

Limited Combustibility

Predominantly mineral-filled with a small controlled organic binder (<5%). Cannot independently sustain a flame once the ignition source is removed. Generates very limited heat and negligible smoke. Satisfies EN 13501-1 A2-s1,d0 — the required standard for most high-rise facades in Europe and the UK post-Grenfell.

Organic <5%

B1

Flame Retardant (DIN 4102)

Significant polymer content (often LDPE) with flame-retardant additives — aluminium trihydrate (ATH), antimony oxide, or halogenated compounds. Self-extinguishes when ignition source is removed per DIN 4102 B1. Does burn when continuously exposed, producing significant smoke and CO. Permitted for low-rise applications only in most modern codes.

Organic 20–40%

Non-FR

Standard / No Fire Rating

Pure or near-pure polyethylene (PE) core — no flame-retardant additives. Burns readily, sustains flame aggressively, propagates fire vertically along the facade at alarming speed, and produces dense black carbon-rich smoke laden with CO. Responsible for numerous catastrophic high-rise fires including Grenfell Tower (2017).

Organic >90%

Critical context — Grenfell Tower, London 2017: 72 people died in a fire that spread up the 24-storey building via ACP rainscreen cladding with non-FR polyethylene cores. The panels acted as a continuous vertical fuel strip. Post-disaster building codes in the UK (BS 8414), Europe, Australia, UAE, and Singapore now mandate A2 or A1 cores on any building above 11–18 m in height.

Section 02

How Fire-Rated Cores Prevent Building Fire Accidents

01
Eliminating the fuel strip from the facade: An A1 core contains no organic carbon fuel. The aluminium skins may buckle under heat, but the mineral core cannot ignite — eliminating the primary mechanism by which fire climbs the exterior of a building.
02
Blocking vertical fire propagation: Non-FR PE cores act as a continuous vertical fuel ladder — a floor-level fire can ignite the PE, which carries a flame up the entire building height within minutes. A2 and A1 cores break this chain entirely. B1 cores significantly slow it but do not eliminate risk on tall buildings.
03
Drastically reducing heat release rate (HRR): PE releases approximately 43–46 MJ/kg — comparable to petrol. A1 mineral cores release effectively zero heat. A2 cores release <3 MJ/m². Lower HRR buys critical evacuation time and limits structural steel temperature rise.
04
Limiting smoke — the primary killer: Over 70–80% of fire deaths are from smoke inhalation, not burns. Non-FR PE produces dense black carbonaceous smoke with CO concentrations of 2,000–8,000 ppm within minutes. A1 and A2 cores produce near-zero smoke, preserving escape route visibility and air quality in evacuation corridors throughout the event.
05
Preventing the cavity flue effect: Rainscreen facades contain an air gap behind the panel. In a non-FR panel fire, this cavity becomes a chimney — superheated gases and burning PE droplets travel upward, igniting at each floor. Mineral cores do not melt or drip flaming liquid, suppressing this dangerous cavity flue mechanism.
06
Maintaining structural integrity of the facade assembly: Burning PE liquefies and drips as flaming liquid, attacking aluminium brackets, rails, and anchor bolts. Mineral cores remain dimensionally stable — keeping panels in place longer and preventing detached burning panels from falling onto evacuating occupants below.
07
Protecting fire compartmentation: A fire-rated core integrated with cavity fire stops ensures the facade does not bypass compartmentation built into floors and party walls — preserving the 30, 60, 90, or 120-minute fire resistance ratings that govern safe evacuation and firefighting operations.
08
Reducing toxic gas generation from FR additives: Some B1 cores use PVC or halogenated compounds which, while slow to ignite, produce hydrogen chloride (HCl) and dioxins when they burn — highly toxic and corrosive gases. A2 and A1 mineral cores produce no such toxicants, making fire events safer for occupants and first responders alike.
09
Meeting full-evacuation time requirements: High-rise evacuations take 30–90 minutes. The combination of zero heat release, no smoke, and no flame propagation from A1 cores provides the time window necessary for complete evacuation before escape routes become untenable — something non-FR PE cannot offer beyond a few minutes.
10
Insurance, legal, and regulatory compliance: Certified fire-rated cores with documented test certificates shift liability appropriately, satisfy fire authority approvals, building warranties, and occupancy permits — protecting developers, building owners, and facade contractors from catastrophic financial and criminal exposure following a fire incident.

Section 03

Core Ingredients — What's Inside Each Classification

Core Type	Primary Ingredients	Flame Retardant Mechanism	Organic %
A1	Aluminium Hydroxide (ATH) 60–70% Magnesite / MgO 15–25% Inorganic binders <5% Mineral fillers (trace)	Endothermic decomposition: ATH releases bound water at ~180°C (Al(OH)₃ → Al₂O₃ + 3H₂O), absorbing heat and diluting oxygen. No organic fuel present.	<1%
A2	ATH 50–65% Magnesium Hydroxide (MDH) 10–20% PE/PP organic binder 3–5% Calcium carbonate filler	Same endothermic mechanism as A1. Tiny polymer binder provides processability but is insufficient in mass to sustain combustion independently.	<5%
B1	LDPE Polyethylene 40–60% ATH Flame Retardant 25–40% Antimony Trioxide (Sb₂O₃) 3–5% HDPE / other polymer 5–10% Halogenated additives (some grades)	Combined endothermic (ATH releases H₂O) and gas-phase inhibition (halogen compounds interrupt free radical chain reactions in the combustion zone). Self-extinguishes per DIN 4102 B1 when ignition removed.	20–40%
Non-FR	LDPE 85–95% HDPE blend 5–10% Pigments / stabilisers <2% No flame retardant additives	No mechanism. Burns with self-sustaining flame. Drips as burning liquid. Calorific value ~43 MJ/kg — comparable to diesel fuel. Black carbon soot from incomplete combustion.	>90%

ATH — The Workhorse of Mineral Flame Retardants: Aluminium Trihydrate (Al(OH)₃) undergoes endothermic decomposition at ~180°C: Al(OH)₃ → ½ Al₂O₃ + 3/2 H₂O. This reaction absorbs significant heat (1,050 J/g), releases water vapour that dilutes the combustion zone, and leaves a thermally stable aluminium oxide residue. Higher ATH loading = better fire performance. A1 cores are essentially engineered around maximising ATH content while maintaining mechanical bond integrity.

Section 04

Laboratory Fire Testing — Process & Temperatures

Key ASTM Standards for ACP & Facade Testing: ASTM E84 (Steiner Tunnel — Surface Burning) · ASTM E119 (Standard Fire Resistance — Time/Temperature Curve) · ASTM E1354 (Cone Calorimeter — HRR & Smoke) · ASTM E162 (Radiant Panel — Flame Spread) · NFPA 285 (Multi-storey Exterior Wall Fire Propagation)

ASTM E84 — The Steiner Tunnel Test (Primary ACP Test)

1

Specimen Prep

ACP cut to 510 mm wide × 7.3 m long. Mounted on tunnel ceiling in test orientation. Conditioned 23°C / 50% RH for minimum 24 hours before test.

2

Ignition

Two 88 kW gas burners ignite the specimen end. Test duration: exactly 10 minutes (600 seconds). Burner zone reaches 815–900°C peak temperature.

3

Flame Spread

Flame front position is recorded every 15 seconds. Flame Spread Index (FSI) = area under flame-front vs. time curve, calibrated against red oak (FSI=100) and cement board (FSI=0).

4

Smoke Measurement

Photometric system (photoelectric cell + light source) across exhaust duct measures % light obscuration every second. SDI = integrated obscuration over 600 seconds vs. red oak reference.

5

NFPA 285 Full-Scale

Full 2-storey wall assembly (4.9 m × 6.1 m). Room fire at 1,055°C simulates window opening. Pass/fail: does flame exit the window and ignite the facade panel above the opening within 30 minutes?

6

Cone Calorimeter (E1354)

100×100 mm specimen under radiant heat (35 or 50 kW/m²). Measures heat release rate (kW/m²), time-to-ignition, CO, CO₂, and mass loss every second. Most data-rich test for research purposes.

ASTM E119 — Standard Fire Curve Temperatures

The E119 furnace follows the formula: T = 345 × log₁₀(8t + 1) + 20 where T is temperature in °C and t is time in minutes.

ASTM E119 / ISO 834 Standard Fire Curve — Key Temperature Milestones

0 min

20°C

20 °C

5 min

556°C

556 °C

10 min

678°C

678 °C

30 min

842°C

842 °C

60 min

927°C

927 °C

120 min

1010°C

1010 °C

240 min

1093°C

1093 °C

Section 05

Smoke Values — The Silent Killer in Detail

Over 70–80% of all fire fatalities result from smoke inhalation — not burns. Smoke toxicity, optical density, CO, and CO₂ are measured continuously during standard fire tests. Here is a complete breakdown by core type:

ASTM E84 — Smoke Developed Index (SDI) by Core [Lower = Safer · Red Oak Reference = 100]

A1 CoreSDI = 0–5

A2 CoreSDI = 5–15

B1 Core (FR)SDI = 35–75

Non-FR PE CoreSDI = 400–800+

ASTM E84 Class A permit limit: SDI ≤ 450 | Best practice for facades above 10 m: SDI ≤ 50

0–5

A1 Core SDI

Virtually no smoke. Only trace water vapour released. Escape routes remain fully visible for the entire fire event duration.

5–15

A2 Core SDI

Minimal smoke from minor binder combustion. Far below any hazardous threshold. Evacuation fully feasible without respiratory protection.

35–75

B1 Core SDI

Moderate smoke. FR additives reduce vs. plain PE. Can impair visibility in enclosed corridors after 4–6 minutes of continuous exposure.

400–800+

Non-FR SDI

Extreme dense black soot-laden smoke. Visibility in escape routes drops to near-zero within 60–90 seconds of ignition.

CO
Carbon Monoxide (CO) — Primary lethal agent: CO binds to haemoglobin 200× more strongly than oxygen. IDLH (immediately dangerous to life): 1,200 ppm. At 200 ppm: headache in 2–3 hours. At 1,200 ppm: unconsciousness in 3 minutes. At 6,400+ ppm: death in 10–15 minutes. Non-FR PE cores generate CO of 2,000–8,000 ppm in enclosed compartment fires. A1/A2 cores produce essentially zero CO.
CO₂
Carbon Dioxide (CO₂) — Asphyxiant & physiological accelerant: CO₂ above 5% causes hyperventilation, paradoxically increasing CO and toxicant uptake rate by 3–5×. At 10%+, loss of consciousness occurs in minutes. Non-FR PE can generate peak CO₂ of 8–15% in poorly ventilated compartments — why occupants far from the flame still succumb to smoke in PE facade fires.
SDI
How the Smoke Developed Index (SDI) is measured: A photoelectric cell and calibrated light source are positioned across the exhaust duct of the Steiner Tunnel. As smoke particles scatter and absorb light, the percentage obscuration is recorded every second over the 600-second test. The area under the obscuration-vs-time curve is integrated using the trapezoidal rule and normalised against the red oak reference result (SDI=100) to produce the final index value. Values are reported to the nearest 5 units per ASTM E84.
HCN
Hydrogen Cyanide from combined building materials: When facade fires ignite adjacent nitrogen-containing materials (foam insulation, carpets, plastics), HCN is generated as a combustion by-product. At 135 ppm HCN causes death in 30 minutes; at 300 ppm in minutes. While the ACP core itself may not generate HCN, the fire spread enabled by non-FR cores creates the conditions for widespread HCN generation from surrounding materials — A1 core facades prevent this secondary cascade by not initiating the fire spread in the first place.

Section 06

ASTM Fire Performance Calculator

🔥 ACP Core Fire & Smoke Estimator

ASTM E84 · E119 · E1354

ACP Core Type

Test Duration (minutes) ASTM E84 = 10 min · ASTM E119 = 30–240 min

Specimen Area (m²) E84 standard specimen = 3.72 m² (510 mm × 7.3 m)

Heat Flux — Cone Calorimeter (kW/m²) Standard: 35 kW/m² (facade) · Severe: 50–75 kW/m²

E119 Furnace Temperature Curve

🔬

SELECT CORE TYPE & PRESS CALCULATE

E119 Furnace Temp

—°C

Flame Spread Index (FSI)

—/ 450

Smoke Developed Index (SDI)

—/ 450

Peak Heat Release Rate

—kW/m²

Est. Peak CO

—ppm

Est. Peak CO₂

—%

ASTM E84 Classification

—

ASTM E84 Classification Reference — Facade Design Guide

Class	FSI Range	SDI Limit	Typical Core	Building Suitability
Class A	FSI 0–25	SDI ≤450	A1, A2 cores	All occupancies · High-rise · Hospitals · Schools
Class B	FSI 26–75	SDI ≤450	B1 FR core	Limited low-rise · Non-critical applications
Class C	FSI 76–200	SDI ≤450	Marginal FR	Restricted use · Interior low-risk only
FAIL	FSI >200	SDI >450	Non-FR PE	Not permitted — any exterior facade application

ACP Core Fire Ratings& ASTM Fire Calculator

ACP Core Classifications Explained

How Fire-Rated Cores Prevent Building Fire Accidents

Core Ingredients — What's Inside Each Classification

Laboratory Fire Testing — Process & Temperatures

Specimen Prep

Ignition

Flame Spread

Smoke Measurement

NFPA 285 Full-Scale

Cone Calorimeter (E1354)

Smoke Values — The Silent Killer in Detail

ASTM Fire Performance Calculator

ACP Core Fire Ratings
& ASTM Fire Calculator