ASTM D6413 Vertical Flame Test for FR Fabric Buyers | KIGI Textile

ASTM D6413 is one of the most frequently referenced vertical flame tests in the flame-resistant textile market. Buyers see the number on fabric data sheets, laboratory reports and protective-clothing specifications, but the meaning is often oversimplified. A report marked “tested to ASTM D6413” does not automatically prove compliance with NFPA 2112, ASTM F1506 or any finished-garment certification program.

The test method produces specific laboratory observations. The applicable product standard or purchasing specification supplies the acceptance limits. Understanding that separation helps buyers compare fabrics correctly, request complete evidence and avoid treating one test result as a universal flame-resistance certificate.

What Is the ASTM D6413 Vertical Flame Test?

Purpose of the Test

The current active edition listed by ASTM is ASTM D6413/D6413M-22, Standard Test Method for Flame Resistance of Textiles (Vertical Test). The method measures how a textile specimen responds to a defined ignition source while held vertically in a controlled, draft-free test area. ASTM identifies afterflame time, afterglow time and char length as the principal measured values.

The method is useful for material development, comparative evaluation and acceptance testing when another specification states how the results are to be judged. It gives buyers a repeatable way to discuss flame response, but only for the test configuration and exposure described by the method.

Materials and Products It Can Evaluate

ASTM D6413 is a textile test method. It may be applied to fabrics, textile products or assemblies when the relevant product specification calls for it. Within industrial protective clothing, it is commonly referenced for woven and knitted FR fabrics, linings, insulation materials and certain garment components.

The tested construction must be identified precisely. Fiber content alone is not enough. Fabric weight, yarn system, weave or knit, color, finish, coating, lamination and laundering history can all change the result.

What ASTM D6413 Does Not Prove

ASTM states that the method describes response to heat and flame under controlled laboratory conditions and should not be used by itself to describe fire hazard or real-world fire risk. A small vertical specimen does not reproduce garment fit, air gaps, seams, closures, body movement or the heat flux of a flash fire.

ASTM D6413 is therefore not:

• A certification program

• A complete NFPA 2112 garment evaluation

• An arc-rating test

• A thermal protective performance test

• A prediction of body-burn percentage

• Proof that every color, finish or production lot performs identically

What Does ASTM D6413 Measure?

Afterflame Time

Afterflame time is the period during which the specimen continues to flame after removal of the ignition source. Reports normally show an individual result for each specimen and may also show an average. A buyer should not accept only a single selected value when the applicable specification requires multiple specimens or reporting by direction.

Afterflame is not the same as the initial exposure time. It begins after the controlled ignition source is removed. It also should not be confused with afterglow, which occurs without visible flame.

Afterglow Time

Afterglow time records glowing combustion after visible flaming has ceased. The damaged area may continue to glow even when no flame is visible. ASTM D6413 measures this behavior, but a product specification may focus its acceptance criteria on other results. Buyers should still retain the afterglow data because it helps explain specimen behavior and investigate unusual damage.

Char Length

Char length describes the extent of damaged material along the specimen after exposure and the method's specified evaluation. It is reported in either SI or inch-pound units according to the reporting system. ASTM warns that the two unit systems should be used independently rather than mixed as though all converted values were exact equivalents.

Char length does not equal flame height, burn time or predicted skin burn. Two fabrics can have similar char lengths while differing in heat transfer, shrinkage, break-open behavior and garment-level performance.

Melting, Dripping and Other Observations

Laboratories may record whether a specimen melts, drips, separates, develops a hole or displays other notable behavior. These observations deserve attention even when the numerical values appear acceptable. Thermoplastic components can shrink or melt away from the flame, and a short char length alone may not represent a desirable protective response.

For example, the NFPA 2112 framework includes material-specific flame-resistance requirements and addresses melting and dripping in addition to numerical limits. Buyers should identify the exact product standard and edition rather than creating a pass statement from D6413 data alone.

How Is ASTM D6413 Testing Performed?

Specimen Identification and Direction

Fabric behavior may differ between machine and cross-machine directions, commonly described for woven fabrics as warp and filling. A useful report identifies the tested direction for every specimen. If the purchasing requirement applies to both directions, the request should say so explicitly.

The report should also identify the material sufficiently to connect the result to the supplied fabric: style number, fiber content, construction, nominal mass per unit area, color, finish, coating or laminate, production lot and sampling date.

Conditioning, Laundering and Other Preprocessing

Preconditioning is critical for FR textiles. An untreated specimen, a specimen after one home-laundering cycle and a specimen after repeated industrial laundering are not equivalent evidence. Washing chemistry, water quality, drying method, contamination and improper use of bleach or softener can change performance.

The buyer should specify the conditioning and durability sequence required by the relevant product standard or end use. The report should state the method, number of cycles and any deviation. “After wash” without a cycle count and laundering procedure is incomplete.

Vertical Mounting and Controlled Exposure

In the test, specimens are mounted vertically and exposed to the method's defined ignition conditions in controlled laboratory surroundings. The laboratory then records the post-exposure flame and glow behavior and determines char length according to the standard.

This article intentionally does not replace the controlled ASTM procedure. Laboratories should use the licensed current standard, calibrated equipment and qualified personnel. Buyers need to understand the reporting logic, not recreate a safety-sensitive flame test from a website summary.

Individual Results and Averages

Averages are convenient, but they can hide variation. A complete buyer review considers:

• Every individual specimen result

• The average reported for each required direction or condition

• The number of specimens

• Any outlier or incomplete burn observation

• Retests and the documented reason for retesting

• Deviations from the referenced method

If two laboratories produce materially different results, do not assume that one number is automatically wrong. ASTM notes that comparative testing may be needed to investigate possible laboratory bias, using sufficiently homogeneous material and an appropriate statistical approach.

How to Read an ASTM D6413 Test Report

Report Review Checklist

• Full standard designation and edition are stated

• Fabric style, composition, construction, weight, color and finish are identifiable

• Production lot or sample traceability is available

• Specimen directions are stated

• Conditioning and laundering method, cycle count and drying route are stated

• Number of specimens is clear

• Individual afterflame values are shown

• Individual afterglow values are shown

• Individual char-length values are shown

• Required averages are shown

• Melting, dripping and other observations are recorded

• Deviations and retests are disclosed

• Laboratory name, report number and test date are present

• The applicable product specification and acceptance criteria are identified separately

Standard Edition and Modifications

Do not accept “ASTM D6413” as the only method description when the contract depends on a particular edition or modification. The active ASTM listing may not be the edition referenced by a product standard. For example, a certification program may incorporate a dated edition and add its own specimen preparation or reporting rules.

A technically complete report separates the base test method from modifications required by NFPA 2112, ASTM F1506, a certification body or a customer specification.

Fabric Identity and Traceability

The report must be traceable to the material being purchased. A passing report for a navy fabric cannot automatically support every fluorescent color, printed version, coated version or lighter-weight construction. Ask the supplier to explain the tested sample's relationship to the quoted production item and how changes are controlled.

Pass/Fail Statement

A laboratory may show “Pass” when it has been given a separate acceptance specification. The report should name that specification, edition and requirement. A D6413 result without an identified acceptance source is data, not a universal compliance decision.

Does ASTM D6413 Have a Universal Pass/Fail Limit?

No. ASTM D6413 is a test method and does not establish one universal limit for every protective textile. Limits come from the product standard, regulation, certification scheme or buyer specification.

For example, NFPA's published material for the 2023 edition of NFPA 2112 states requirements for specified garment materials tested through its flame-resistance section, including a char length of not more than 100 mm (4 in.), afterflame of not more than 2 seconds, and no melting and dripping for the materials addressed by that provision. The exact requirement depends on material category and the incorporated text, so procurement and certification decisions must use the complete current NFPA document and applicable amendments.

ASTM F1506 serves a different hazard and product context: flame-resistant and electric-arc-rated protective clothing for workers exposed to momentary electric arcs and related thermal hazards. A buyer must not copy an NFPA 2112 criterion into an ASTM F1506 purchase order without confirming the intended hazard, standard edition and complete set of requirements.

The safest wording is: test according to ASTM D6413/D6413M, evaluate according to the named product specification and edition.

What Affects ASTM D6413 Results?

Fiber and FR Technology

Inherent FR fibers and flame-retardant-treated fibers use different protection mechanisms. Blends can combine thermal stability, strength, moisture management and cost, but the final result belongs to the complete fabric construction, not to the fiber name alone.

Fabric Construction and Weight

Yarn size, density, weave, knit structure and mass per unit area affect oxygen access, dimensional stability and damage propagation. Heavier fabric is not automatically better: weight can improve some performance aspects while increasing heat stress, and it cannot substitute for testing.

Dyeing, Finishing, Coating and Lamination

Dyes, softeners, water repellents, binders, coatings, membranes and adhesives can alter ignition, melting, dripping or char formation. Any finish change should be reviewed for its effect on the tested construction. Laminated materials may need evaluation as the actual composite rather than as an isolated face fabric.

Laundering, Contamination and Wear

Improper bleach, oxidizing chemicals, hard-water deposits, oils and other contaminants can reduce protection or create a secondary fuel source. Abrasion and garment wear can lower fabric mass and expose damaged areas. Buyers should connect laboratory durability conditioning with real care instructions and service life.

How Buyers Should Specify ASTM D6413 Testing

Use the following wording as a starting point, then align it with the applicable product standard and certification program:

Before sending this language to a supplier, replace every bracketed field. A purchasing specification with blank end-use assumptions will still produce ambiguous evidence.

Common Purchasing Mistakes

Asking Only for an “FR Certificate”

The phrase does not identify the test, product standard, material, edition, durability condition or certification scope. Ask for the actual report and the applicable conformity evidence.

Comparing Only Average Char Length

An acceptable-looking average may conceal a high individual value, one-direction failure or irregular specimen behavior. Review individual data and the acceptance rules of the named product standard.

Ignoring Laundering History

Initial performance does not establish durability. Specify the required care method and cycle count, especially for treated FR cotton and blended workwear fabrics.

Treating D6413 as an Arc Rating

ASTM D6413 does not produce an ATPV, EBT or arc rating. Arc-rated materials require the applicable arc-test method and performance specification. See [ASTM F1959 arc rating guide - internal link] and [FR vs. AR fabric guide - internal link].

Assuming Fabric Testing Certifies the Garment

Garment design, seams, closures, labels, reflective materials and other components can introduce separate requirements. For flash-fire protection, connect fabric development with [NFPA 2112 garment requirements - internal link] and [ASTM F1930 manikin testing - internal link].

ASTM D6413 Frequently Asked Questions

Is ASTM D6413 for Textiles or Plastics?

ASTM D6413 is for the vertical flame resistance of textiles. It is sometimes mistyped as ASTM D6341. ASTM D6341 is unrelated to protective textiles; it addresses the linear coefficient of thermal expansion of plastic lumber and plastic lumber shapes.

Does a Shorter Char Length Always Mean Better Protection?

Not necessarily. Char length is one bench-scale result. Thermal heat transfer, shrinkage, break-open, fabric weight, garment construction and the intended hazard also matter.

Is Afterglow the Same as Afterflame?

No. Afterflame involves visible flaming after the ignition source is removed. Afterglow is glowing combustion after visible flame has ended.

Can ASTM D6413 Predict Body-Burn Percentage?

No. Predicted body-burn percentage is associated with an instrumented thermal-manikin evaluation such as ASTM F1930 under the applicable program. D6413 does not reproduce a full garment or flash-fire exposure.

Can One Test Report Cover Every Color?

Only when the governing program and supplier's controlled product family allow that conclusion. Color, dye recipe and finishing changes may affect results. Buyers should ask how the tested sample represents the ordered colors.

Should Buyers Specify ASTM D6413/D6413M-22 Every Time?

Use the edition required by the applicable product standard, certification program or contract. The current active ASTM edition is important, but an incorporated product standard may reference a particular dated edition. Record both clearly.

Request FR Fabric Testing and Development Support

The best ASTM D6413 request begins with the end use. Tell us whether the fabric is intended for oil and gas workwear, electrical protective clothing, utility uniforms or another industrial application. Include the target standard, fabric construction, weight range, color, finish, laundering route and required evidence.

KIGI Textile can support FR fabric construction review, sample development and coordination of buyer-defined testing. Final product selection, certification and workplace protection must be confirmed by the responsible manufacturer, employer, accredited laboratory or certification body.

• ASTM D6413/D6413M - Standard Test Method for Flame Resistance of Textiles (Vertical Test)

• NFPA 2112, 2023 Edition - Tentative Interim Amendment 23-1

• OSHA interpretation on certified flame-resistant clothing and NFPA 2112