Protection specified by hazard type
Covering flame, molten metal, arc flash and thermal transmission, with the protection levels defined in each standard explained.
Eight hazards
Most working environments combine several hazards: furnace work involves molten metal, radiant heat and contact heat at the same time. Categories follow the dominant hazard, and selection must account for combinations.
Flame & flash fire
Short-duration flame contact and flash fire from flammable gases. Requires no afterflame, no melting and limited heat transmission.
Molten metal splash
Aluminium and iron splash that may penetrate the fabric. Requires high mass per unit area, penetration resistance and no skin adhesion.
Arc flash
Instantaneous heat and pressure from an electric arc. Requires high incident energy tolerance without rupture or afterflame.
Convective, radiant and contact heat
Hot gas streams, high-temperature radiant sources and hot solid surfaces. The three transmit heat differently and are tested differently.
Welding spatter
High-velocity slag and droplets. Requires burn-through and adhesion resistance while retaining mobility.
Static accumulation
Static charge building and discharging into flammable gas or dust. Requires a continuous conductive path that survives washing.
Low visibility
Being seen in traffic, at night and in poor weather. Requires fluorescent colour performance and retroreflection together.
Liquid chemical penetration
Acid, solvent and oil splash and penetration. Requires coating or membrane barrier performance and sealed seams.
Flame & flash fire: no afterflame, no melting
Flash fire is short in duration but high in heat flux. The primary requirement on the fabric is no afterflame and no melting: molten droplets adhere to skin and cause more severe injury than the flame itself.
Four requirements on the fabric
- Self-extinguishing — combustion stops once the ignition source is removed, with controlled afterflame and afterglow
- No melting — carbonises at high temperature rather than melting, avoiding adhesion of molten material to skin
- Char integrity — forms an insulating char rather than rupturing and exposing inner layers
- Durability — the above is not significantly reduced by washing or abrasion
The principal difference between inherent and treated FR lies in performance retention after washing: treated FR declines progressively with repeated washing, while inherent FR does not.
Interpreting the standards
| Standard | Core criteria | Notes |
|---|---|---|
GB 8965.1-2020 | Afterflame / afterglow time, char length | Chinese FR clothing standard, grades A and B, A being the higher requirement |
EN ISO 11612 | Code A1 / A2 | Code A is mandatory; A2 adds a surface ignition test to A1 |
NFPA 2112 | 50% burn time | US industrial flash fire standard, instrumented manikin body burn assessment |
Molten metal: penetration, not temperature alone
Molten metal strikes the fabric as high-temperature droplets. The principal risks are penetration and adhesion, and injury severity increases rapidly with penetration depth. Wool and aramid — which carbonise rather than melt — are the established fibre systems for metalworking.
D and E levels in EN ISO 11612
D and E correspond to aluminium and iron respectively. The number indicates the level of splash mass tolerated: a higher number denotes a higher level of protection.
- Code D1 / D2 / D3
- Protection against molten aluminium splash. Tested to ISO 9185; a higher level indicates a greater mass of aluminium that can be poured without producing a second-degree burn.
- Code E1 / E2 / E3
- Protection against molten iron splash. Iron behaves differently owing to its higher melting point and density, so it is graded separately and is not interchangeable with D.
- Why they are separate
- Temperature, fluidity and adhesion differ markedly between aluminium and iron; the same fabric may perform very differently in the two tests. Flame resistance alone does not describe this performance.
Metalworking positions generally also require one or more of level B (convective heat), C (radiant heat) and F (contact heat). EN ISO 11612 requires level A plus at least one heat transmission criterion.
Arc flash: incident energy, not flame resistance rating
An arc releases high energy within tens of milliseconds. The relevant measure is the fabric arc rating, expressed in cal/cm² or kJ/m².
ATPV and EBT
- ATPV
- Arc Thermal Performance Value — incident energy at which there is a 50% probability of second-degree burn
- EBT
- Energy Breakopen Threshold — incident energy at which the fabric ruptures
- Rating
- The lower of the two values becomes the fabric arc rating
Two test methods, not interchangeable
- IEC 61482-1-1
- Open arc method, determining ATPV / EBT as an energy value
- IEC 61482-1-2
- Box test method, classifying APC class 1 or class 2
- Note
- The two cannot be converted into one another; ASTM F1959 is commonly used in North America
Selection begins with the prospective fault current and clearing time at the work location to establish the required protection energy, from which the fabric arc rating follows. NFPA 70E and DL/T 320 set out the corresponding calculation and selection methods.
Flame resistance ≠ thermal insulation
Flame resistance describes whether a fabric continues to burn; thermal insulation describes how long heat takes to reach the skin. A fabric that does not burn can still cause serious injury if heat passes through quickly.
| Heat type | Typical situations | Test method | EN ISO 11612 level | What the value means |
|---|---|---|---|---|
| Convective heat | Direct flame and hot gas streams | ISO 9151 |
B1 – B3 |
TPP value: time to second-degree burn, longer is better |
| Radiant heat | Furnace openings, ladles, radiant sources at distance | ISO 6942 |
C1 – C4 |
RHTI 24 / RHTI 12: heat transmission level and time |
| Contact heat | Contact with hot solid surfaces, tools, castings | ISO 12127 |
F1 – F3 |
Contact time threshold to second-degree burn |
| Molten metal splash | Aluminium and iron splash | ISO 9185 |
D1–D3 / E1–E3 |
Mass of liquid metal tolerated |
What the measures distinguish
Flame resistance rating and thermal insulation are independent measures: the former confirms the fabric does not continue to burn, the latter reflects the rate of heat transmission.
Selection sequence
Establish the dominant heat transmission type, confirm the required level, then select the fibre system and weight.
Describe the working environment
Temperature, ignition sources, metal type, operating current and laundering method allow us to break the hazard down and propose a blend.