Have you ever seen labels like “flame retardant” or “fireproof” on appliances, outlets, building materials, or even children’s pajamas? And silently wondered: Does this stuff really not catch fire?
The answer is: No, they aren’t fireproof. Rather, they are “less likely to ignite” or “self-extinguish once ignited.” The science behind this is what we’ll discuss: “flame retardant ratings.” This isn’t a marketing gimmick but a rigorous scientific standard—the key to buying you precious escape time in a fire.
First, let’s dispel a common misconception: apart from a few inorganic materials like stone and steel, most substances will burn under sufficiently high temperatures and oxygen conditions. What we mean by “flame retardancy” is imparting one or more of the following properties to materials through physical or chemical means:
Flame retardancy ratings quantify this“fire resistance”through standardized testing methods.。
In plastics, electronics, and related fields, the most renowned and widely adopted benchmark is the UL94 standard certified by UL (Underwriters Laboratories) in the United States. It assigns ratings through a series of rigorous combustion tests.
You can think of UL94 ratings as a “combustion exam score,” with the following primary “score tiers” from highest to lowest:
Test Performance: One of the highest levels. The sample undergoes two 10-second flame exposures. After each exposure, the flame extinguishes spontaneously within 10 seconds, with absolutely no ignitable particles dripping.
Layman’s Terms: Extremely “aloof”—it flees at the first sign of fire, refuses to linger, and leaves no “trail” (sparks).
Applications: High-quality power strips, phone chargers, routers, computer power supplies, and other AC-powered, heat-generating devices should meet V-0 standards. This is a critical defense for household electrical safety.
Example: As shown in the image, the materials used in cable cold-shrink sleeves produced by Zhejiang Enwei Electric Co., Ltd. employ V-0 rated flame-retardant materials.
Test Performance: Similarly extinguishes within 30 seconds after flame removal, but burning particles that could ignite cotton are not permitted during combustion.
Layman’s Terms: Safer than V-2, does not drop sparks.
Test Performance: Withstands two 10-second flame exposures and self-extinguishes within 30 seconds after flame removal. However, burning particles may drip during combustion and potentially ignite underlying cotton.
Layman’s terms: Self-extinguishes after flame removal but “drops sparks.” These sparks may cause secondary fires in specific environments (e.g., near paper or synthetic fabrics).
Applications: Suitable for internal structural components or external parts with relaxed drip requirements.
Test Performance: A horizontally placed specimen burns at a slow rate, with the burn length not exceeding the specified value.
Layman’s Terms: It can burn, but slowly. Suitable for products with extremely low fire risk, such as certain toys or non-critical structural components.
Note: Many cheap, uncertified power strips and charger housings may use this grade or substandard materials, posing significant safety hazards!
Beyond these, higher-grade “expert-level” ratings like 5VA and 5VB require passing stricter vertical panel tests, typically used for large equipment housings or extremely high-risk applications.
The UL94 standard primarily evaluates material flame retardancy through two test methods: vertical burning and horizontal burning.
1.Sample Preparation: Fabricate standard-sized strip specimens from the material (typically 125mm×13mm).
2.Test Environment：Conducted in a well-controlled laboratory setting to avoid airflow interference.
3.Flame Application：Utilize a standardized Bunsen burner with flame height (methane flame) set to 20mm and blue inner flame height at 10mm.
4.Test Procedure：Apply flame 10mm above the specimen base for 10 seconds, then remove. Record combustion behavior.
5.Repeat Test：After flame extinguishes (or 30 seconds later), reapply flame for 10 seconds.
6.Observation & Documentation：Record flame extinguishment time, presence of burning droplets, and ignition of underlying cotton.
UL94 testing provides a relatively objective flame-retardant performance evaluation system by simulating material behavior when ignited under different orientations (horizontal, vertical) and flame intensities. V-0 grade outperforms V-1, V-1 outperforms V-2, while 5VA/5VB represent higher flame-retardant levels. When selecting electronic products, especially high-power or long-operating devices, verifying that plastic components use high-flame-retardant-rated materials is a crucial safety measure.
| Grade | Test Method | Flame Duration | Dripping | Application |
| V-0 | Vertical burning | Flame extinguishes within 10 seconds per test | No burning drips allowed | High-end appliances, automotive components |
| V-1 | Vertical burning | Flame extinguishes within 30 seconds per test | No burning drips allowed | Industrial products, electrical equipment |
| V-2 | Vertical burning | Flame extinguishes within 30 seconds per test | Burning droplets permitted | General appliance housings |
| 5VA | Panel Vertical Burning | Flame extinguishes within 60 seconds, no holes allowed | No burning drips allowed | High-safety equipment enclosures |
| 5VB | Panel Vertical Burning | Flame extinguishes within 60 seconds, holes permitted | No burning drips allowed | High-safety equipment enclosures |
| HB | Horizontal burning | Burn rate <75mm/min (3mm thickness) | No restrictions | General materials, daily necessities |
Plastics are hydrocarbons and excellent fuels. How do we make them flame-retardant? Scientists primarily employ the following mechanisms:
1.Suffocation Effect：Flame retardants decompose when heated, releasing non-flammable gases (e.g., nitrogen, carbon dioxide) that dilute oxygen concentration, “smothering” the flame.
2.Cooling Effect：Certain flame retardants(like aluminum hydroxide) absorb significant heat during decomposition, lowering the material’s surface temperature to achieve a cooling effect.
3.Forming a Thermal Barrier Layer：This is a highly effective method. Flame retardants induce the formation of a porous, dense carbon layer on the burning surface of the plastic. This carbon layer acts like“armor,”isolating the internal plastic from oxygen and flames while preventing further heat transfer.
4.Interrupting Chain Reactions:In the gas phase, flame retardants capture free radicals essential for combustion, thereby interrupting the chain reaction of burning.
1.Home Appliance Safety: If the casings of rice cookers, outlets, and chargers are rated V-0, it means that in the event of an internal short-circuit fire, the flames will struggle to burn through the casing and ignite other items.
2.Electronic Devices: The flame-retardant rating of the circuit board materials inside your phone, computer motherboard, and power bank directly affects whether the fire can be effectively controlled during battery thermal runaway.
3.Home Renovation: Using Class B1 materials for ceilings, wall panels, and electrical conduits can buy you precious minutes for escape and firefighting during the initial stages of a home fire.
4.Public Transportation: Seats, interior panels, and wiring in airplanes, high-speed trains, and subways must meet the highest flame retardant standards—a lifeline for public safety.
Understanding flame retardancy ratings is crucial, but maintain scientific rationality:
Flame retardancy does not equate to harmlessness: Some older flame retardants may release toxic gases when burning. However, with technological advancements, eco-friendly halogen-free flame retardants have become mainstream.
It serves only as a “delay tactic”: The purpose of flame retardancy is to slow combustion, creating conditions for escape—not to render objects indestructible in intense flames. No material can withstand prolonged exposure to extreme heat.
Comprehensive protection is key: Safety is a system. Beyond material flame retardancy, installing smoke alarms, equipping fire extinguishers, and planning escape routes are equally vital.
As consumers, how should we choose? (Practical advice)
Theory is less valuable than practical application. Keep these points in mind:
The quality of flame-retardant performance often determines outcomes during emergencies. When purchasing electrical components, cable accessories, appliance housings, and similar products,prioritizing items made with materials that pass high-level flame-retardant tests (like UL94 V-0) means adding an extra layer of protection for your equipment, environment, and even lives.
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