UL 723 : 2018

Test for Surface Burning Characteristics of Building Materials

What UL 723 means for building fire safety

UL 723 is a standardized surface burning test used to evaluate how building materials behave under controlled fire exposure in a tunnel-type test. It reports two core values that help teams compare products and document compliance.

1. Flame Spread Index (FSI): indicates how rapidly flame spreads across the material surface under test conditions.
2. Smoke Developed Index (SDI): indicates the level of smoke generated during the test.
3. Why it matters: these indices support consistent material selection, specification, and compliance documentation.

Standardized testing vs inconsistent fire performance claims

1. Without UL 723 testing: “fire resistant” claims can be difficult to compare across brands and material types.
2. With UL 723: materials are tested under consistent conditions so results are easier to use for approvals and specifications.
3. Outcome: reduced ambiguity when selecting interior finish materials for safety and compliance needs.

Video credit: CertainTeed on YouTube.

Core building blocks of UL 723

1. Test apparatus: a standardized tunnel setup where the test specimen is installed in a consistent orientation.
2. Controlled flame exposure: the ignition source and airflow are controlled to keep tests comparable.
3. Flame spread measurement: flame progression is tracked to generate the Flame Spread Index (FSI).
4. Smoke measurement: smoke production is monitored to generate the Smoke Developed Index (SDI).
5. Test report output: documented results used for submittals, procurement decisions, and compliance files.

Video credit: SGS Farmingdale on YouTube.

High-value use cases of UL 723

1. Interior wall and ceiling finishes: panels, laminates, insulation facings, decorative systems, and coatings.
2. Commercial buildings: offices, schools, hospitals, malls, airports, and public assembly spaces.
3. Industrial facilities: specification of interior finishes where validated documentation is required.
4. Product development: improving formulations to reduce flame spread and smoke output.
5. Procurement and compliance: comparing products using objective indices from a consistent test method.

Video credit: LabTest Certification Inc. on YouTube.

Integration with related standards and codes

1. UL 723 is commonly referenced alongside other surface burning test methods used in building safety conversations and documentation.
2. It is frequently used to support building code requirements for interior finish materials.
3. It can be used as part of a broader fire safety program alongside other tests that measure different fire behaviors.

How to interpret UL 723 results

1. Lower FSI: typically indicates slower surface flame spread under the test conditions.
2. Lower SDI: typically indicates reduced smoke generation under the test conditions.
3. Use results correctly: UL 723 results are comparative indices from a standardized method, not a full prediction of all real-world fire scenarios.

Deployment timeline and cost benchmarks

1. Week 1: confirm which products require UL 723 documentation and what acceptance thresholds apply.
2. Weeks 2–4: coordinate sampling, mounting requirements, and lab scheduling.
3. Weeks 4–6: complete testing, receive reports, and prepare compliance documentation for submittals.
4. Best practice: maintain a current report library so teams do not repeat testing unnecessarily.

Common pitfalls and how to avoid them

1. Assuming one test equals “fireproof”: UL 723 evaluates surface burning characteristics only.
2. Ignoring smoke: SDI can matter as much as flame spread for safety and acceptance.
3. Not matching installation method: ensure the tested configuration aligns with the real intended use.
4. Using outdated reports: confirm the report matches the exact product build and is current.

Case study: faster approvals for interior finish packages

A project team standardized interior finish selection using UL 723 reports for all major finish categories.

1. Submittals were accepted faster because documentation was consistent.
2. Fewer substitutions were required mid-project due to earlier compliance validation.
3. Risk of non-compliant finishes dropped significantly during inspections.

Next steps and additional resources

1. Identify which material categories require UL 723 documentation for your projects.
2. Confirm thresholds and approval expectations with the applicable authority or code requirements.
3. Maintain a library of current UL 723 test reports for procurement, audits, and submittals.
4. Link UL 723 with other fire safety standards in your standards library for complete coverage.

Frequently Asked Questions

1. What does UL 723 test?
It evaluates surface flame spread and smoke development characteristics of building materials.

2. What are FSI and SDI?
FSI is the Flame Spread Index and SDI is the Smoke Developed Index reported from the test.

3. Where is UL 723 used?
In material selection, building specifications, compliance documentation, and safety approvals.

4. Does UL 723 mean a material is fireproof?
No. UL 723 is a surface burning characteristics test and should be used alongside other fire safety requirements as applicable.

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