ISO 14935:2020

Overview

ISO 14935:2020 specifies a standardized laboratory method to assess the persistence of a flame applied to the edge of a non‑flammable wick (aluminosilicate plate) immersed in fire‑resistant fluids. It is one of four basic flammability tests used to characterise fire‑resistant hydraulic and related fluids. The test measures how long a small flame continues on the soaked wick after removal of an igniting flame, and is used to support product specifications, quality control and safety assessment. ISO 14935:2020 does not address spray behaviour and excludes certain liquids (e.g., HFAE and HFAS).

Key topics and technical requirements

• Test principle: A non‑flammable aluminosilicate plate is soaked, clamped in a brass reservoir and ignited at the plate edge. After removal of the igniting flame the continued burning time is measured.
• Test matrix: Five exposure times (2 s, 5 s, 10 s, 20 s, 30 s); six determinations per exposure time; calculate a mean for each exposure time; report the highest mean as the flame mean persistence.
• Apparatus & dimensions (selected requirements from the standard):
  • Reservoir: brass, ~200 mm × 25 mm × 20 mm, clamp span 180 mm ± 2 mm.
  • Test plate: aluminosilicate, width 25 mm ± 1 mm, thickness 2 mm ± 0.2 mm, length 195 mm ± 5 mm.
  • Burner nozzle: 0.6 mm diameter; ignition flame height 25 ± 1 mm; nozzle‑to‑plate distance 6.5 mm ± 0.5 mm.
  • Propane fuel (commercial quality per ISO 9162) and a regulated supply.
• Conditions & procedure: Tests at 18–22 °C in still air, soak plates ≥10 min, drip‑off time 300 ± 10 s before ignition, complete all five exposure series within 2 hours.
• Result expression & pass criterion: Report the largest mean (to 0.1 s) as flame mean persistence. The test is used as a yes/no definition where an average burning time < 60 s is considered passing.
• Referenced standards: ISO 3170 (sampling), ISO 9162 (propane), related spray tests ISO 15029‑1 and ISO 15029‑2; ISO 12922 references this method for hydraulic fluid specifications.

Applications and users

• Who uses ISO 14935:2020
  • Petroleum and hydraulic fluid manufacturers (R&D and QC)
  • Independent testing laboratories and conformity assessment bodies
  • Procurement/specification engineers and OEMs of hydraulic systems
  • Safety and compliance teams evaluating fire resistance
• Practical applications
  • Acceptance testing for fire‑resistant hydraulic fluids
  • Product development and formulation screening to reduce wick flame persistence
  • Verifying compliance with industry specifications (e.g., ISO 12922)
  • Generating data for safety documentation and risk assessments

Related standards

• ISO 15029‑1 / ISO 15029‑2 - tests for spray flammability behaviour
• ISO 12922 - specification for flame‑retardant and less flammable hydraulic fluids
• ISO 3170 - manual sampling of petroleum liquids
• ISO 9162 - propane quality requirements

Keywords: ISO 14935:2020, wick flame persistence, fire‑resistant fluids, flammability testing, hydraulic fluids, aluminosilicate plate, flame mean persistence.