Flash Point Considerations: Shipping Flammable Flavor Concentrates Safely

Author: R&D Team, CUIGUAI Flavoring

Published by: Guangdong Unique Flavor Co., Ltd.

Last Updated:  Jan 21, 2026

Pensky-Martens Flash Point Testing

Introduction: The Invisible Risk in the Aroma

For manufacturers of e-liquids, the pursuit of the perfect flavor profile—that precise balance of strawberry and cream, or tobacco and caramel—is paramount. As a flavor concentrate manufacturer, our role is to supply the complex, highly concentrated building blocks that make those final products possible. However, the very chemistry that allows these concentrates to carry intense aromas and combine seamlessly with vegetable glycerin (VG) and propylene glycol (PG) often introduces a significant logistical challenge: flammability.

The logistics of the vaping industry are under constant scrutiny. Moving concentrated flavorings across borders and oceans isn’t just about speed; it’s about rigid adherence to international safety standards. The central metric governing the safety of shipping these volatile mixtures is the Flash Point.

Ignoring flash point data isn’t merely a paperwork oversight; it is a direct violation of international law, a severe safety hazard for logistics personnel, and a guaranteed way to have critical shipments seized by customs or rejected by carriers.

This article serves as an authoritative, deeply technical guide for e-liquid manufacturers, procurement managers, and logistics coordinators. We will dissect the science of flash point, explore the labyrinth of international regulatory bodies (IATA, IMDG, DOT), explain the crucial classification system for “Class 3 Flammable Liquids,” and provide actionable strategies for compliant, efficient shipping of flavor concentrates. Understanding these dynamics is essential for maintaining an uninterrupted supply chain in the competitive e-cigarette market.

Section 1: The Science: What Exactly IS Flash Point?

Before diving into regulations, we must establish a precise scientific definition of flash point, distinct from other thermal properties like boiling point or auto-ignition temperature.

1.1 The Technical Definition

The flash point of a volatile material is the lowest temperature at which its vapors will ignite if given an ignition source.

It is crucial to understand that the liquid itself does not burn. Flammability is driven by the vapors the liquid gives off. As the temperature of a flavor concentrate rises, the kinetic energy of its molecules increases, causing more molecules to escape the liquid phase and enter the vapor phase immediately above the surface.

When the concentration of this vapor in the air reaches a specific threshold—known as the Lower Flammable Limit (LFL) or Lower Explosive Limit (LEL)—the mixture becomes ignitable. The temperature at which this precise vapor concentration is achieved is the flash point. If an ignition source (a spark, an open flame, static electricity) is introduced at or above this temperature, the vapor will “flash,” or ignite momentarily.

1.2 Flash Point vs. Fire Point vs. Auto-Ignition

It is vital not to confuse flash point with related concepts:

• Flash Point:The vapor ignites briefly but may not sustain combustion because the vapor isn’t being generated fast enough to feed the fire.
• Fire Point:Usually a few degrees higher than the flash point, this is the temperature at which the liquid produces vapor rapidly enough to sustain continuous combustion for at least five seconds after ignition.
• Auto-Ignition Temperature:A much higher temperature at which the substance will spontaneously ignite without an external ignition source.

For shipping regulations, the flash point is the definitive metric because it represents the minimum threshold for a fire hazard during transport conditions.

1.3 Why E-Liquid Flavor Concentrates Are Often Flammable

Flavor concentrates for e-liquids are rarely single chemical entities. They are complex solutions. The active flavor compounds (esters, aldehydes, ketones, pyrazines) are often highly potent and must be dissolved in a carrier solvent to be usable.

While Propylene Glycol (PG) is a common carrier and has a relatively high flash point (~104°C / 219°F), making it generally non-regulated for flammability, many potent flavor extracts require stronger solvents.

The primary culprit for low flash points in flavor concentrates is Ethanol (Ethyl Alcohol). Ethanol is an excellent solvent for extracting natural flavors and carrying volatile aromatics. However, pure ethanol has a flash point of approximately 13°C (55°F). Even when diluted in a concentrate, a significant percentage of ethanol can easily drag the entire mixture’s flash point down below regulatory thresholds.

Other common flavor volatiles, such as Ethyl Acetate (used for fruity/sweet notes), have very low flash points (around -4°C / 25°F) in their pure form. Even small percentages of these highly volatile compounds can significantly impact the overall flammability classification of a concentrate.

1.4 Measuring Flash Point: The Closed-Cup Standard

How is this temperature determined? Regulatory bodies almost universally require the use of Closed-Cup Test Methods.

In an open-cup test, vapors are allowed to dissipate into the ambient air. In a closed-cup test, the sample is heated in a sealed vessel containing air. This simulates conditions in a sealed shipping container where vapors can accumulate. Because the vapors are contained, closed-cup tests almost always result in a lower (more conservative and safer) flash point reading than open-cup tests.

Standard test methods referenced by international regulations include:

• ASTM D93:Pensky-Martens Closed Cup Tester (common for fuel oils and liquids with suspended solids).
• ASTM D3278or D3828: Small Scale Closed Cup devices (often used for paints, lacquers, and flavorings where smaller sample sizes are preferred).

For shipping flavor concentrates, relying on an open-cup value is a critical error that can lead to misclassification and regulatory penalties.

Section 2: The Regulatory Landscape: Who Makes the Rules?

Shipping flammable liquids isn’t governed by a single entity. It is a complex web of international agreements implemented by national authorities and specific transport modes. Understanding this hierarchy is essential for global compliance.

At the apex sits the United Nations (UN). The UN Committee of Experts on the Transport of Dangerous Goods develops the UN Recommendations on the Transport of Dangerous Goods—Model Regulations. This “Orange Book” provides the framework that most nations and modal authorities adopt to ensure consistency.

CITATION 1: For detailed insights into the foundational framework for global dangerous goods transport, refer to the United Nations Economic Commission for Europe (UNECE), which publishes the “UN Recommendations on the Transport of Dangerous Goods – Model Regulations.” Available at: https://unece.org/transport/dangerous-goods

Below the UN framework, specific organizations govern different modes of transport:

1. Air Transport (IATA/ICAO):The International Air Transport Association (IATA) publishes the Dangerous Goods Regulations (DGR), based on the International Civil Aviation Organization (ICAO) technical instructions. These are the strictest regulations because the risks of fire on an aircraft are catastrophic. Most international shipments of high-value flavor concentrates move via air.
2. Sea Transport (IMDG):The International Maritime Organization (IMO) publishes the International Maritime Dangerous Goods (IMDG) Code. This governs containerized ocean freight. While less restrictive on quantities than air transport, it has stringent requirements for stowage and segregation within containers.
3. Road and Rail (National/Regional):

• United States:The Department of Transportation (DOT), specifically the Pipeline and Hazardous Materials Safety Administration (PHMSA), governs transport via Title 49 of the Code of Federal Regulations (49 CFR).
• Europe:The Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) governs road transport spanning most of the European continent.

A flavor manufacturer must classify their product so that it complies with all regulations it will encounter during its journey. A shipment originating in the US, traveling by truck to an airport, flying to Germany, and trucking to a final destination must simultaneously comply with DOT, IATA, and ADR regulations.

Section 3: Classifying Flammable Liquids (Class 3)

Under the UN system, dangerous goods are divided into nine classes. Flammable liquids fall squarely into Class 3.

If a flavor concentrate has a closed-cup flash point of 60°C (140°F) or below, it is generally considered a Class 3 Flammable Liquid for transport purposes.

However, simply knowing it’s “Class 3” is insufficient. The degree of danger must be further defined by assigning a Packing Group (PG). The Packing Group determines the type of packaging required, the maximum quantities allowed per package, and the labeling mandates.

Packing Groups are assigned based on a combination of Flash Point and Initial Boiling Point:

Flammable Liquids Packing Groups Infographic

• Packing Group I (High Danger):Any flash point, but an initial boiling point of ≤ 35°C (95°F). (Rare for flavor concentrates, more common for very volatile solvents like pure diethyl ether).
• Packing Group II (Medium Danger):Flash point < 23°C (73.4°F) AND initial boiling point > 35°C. (Very common for alcohol-based flavor concentrates).
• Packing Group III (Low Danger):Flash point ≥ 23°C (73.4°F) and ≤ 60°C (140°F), AND initial boiling point > 35°C. (Common for concentrates with lower alcohol content or higher PG ratios).

The Crucial 23°C (73.4°F) Threshold

The distinction between PG II and PG III is massive in terms of logistics costs. A flash point of 22°C forces a product into Packing Group II, which significantly lowers the maximum quantity permitted aboard passenger and cargo aircraft compared to a product with a flash point of 24°C (Packing Group III).

For a flavor manufacturer, precise formulation and testing around this 23°C threshold is a critical aspect of product development logistics.

Section 4: The Importance of Accurate Safety Data Sheets (SDS)

The communication tool for this technical data is the Safety Data Sheet (SDS). As a manufacturer, it is our legal obligation to provide an accurate, globally harmonized SDS for every mixture we create.

For e-liquid manufacturers receiving our goods, the SDS is not just a document to file away; it is the blueprint for compliant shipping of their finished goods (if they remain flammable) and for ensuring workplace safety.

CITATION 2: The requirements for Safety Data Sheets, including the standardized 16-section format and the criteria for classification, are detailed in the “Globally Harmonized System of Classification and Labelling of Chemicals (GHS),” published by the United Nations. Information on GHS implementation can also be found via the Occupational Safety and Health Administration (OSHA) in the US. Source: https://www.osha.gov/dsg/hazcom/ghsguideoct05.pdf

Section 9 (Physical and Chemical Properties) and Section 14 (Transport Information) of the SDS are paramount regarding flash point.

• Section 9must state the specific closed-cup flash point value. “Not Determined” is unacceptable for mixtures containing known flammable solvents.
• Section 14translates that data into shipping language: The UN Number (e.g., UN 1197, EXTRACTS, FLAVOURING, LIQUID), the Hazard Class (Class 3), and the Packing Group (II or III).

If an SDS is inaccurate—for example, listing a PG II item as PG III due to sloppy testing or reliance on open-cup data—the receiving party who then re-ships that product using the erroneous data inherits the liability for undeclared dangerous goods.

Section 5: Packaging and Labeling Requirements

Once a flavor concentrate is identified as Class 3, it cannot be shipped in standard cardboard boxes with generic tape. It requires UN-Specification Packaging.

These packages (boxes, drums, jerricans) have been rigorously tested (drop tests, stack tests, pressure tests) to ensure they can withstand the rigors of transport without leaking, even if subjected to pressure changes in an airplane cargo hold.

5.1 Identifying UN Packaging

UN packaging bears a specific code marked permanently on the exterior, such as: UN 4G/Y1.4/S/23/USA/M1234.

• 4G:Fiberboard box.
• Y:Tested for Packing Groups II and III. (An ‘X’ would denote PG I, II, and III; a ‘Z’ only PG III).
• 4:Maximum gross mass in kilograms the box is tested for.

Using a non-UN box for a hazardous shipment is an immediate compliance failure.

5.2 Labeling and Marking

The exterior of the package must clearly display:

• The Class 3 Flammable Liquid Hazard Label:The distinct red diamond with the flame symbol and the number ‘3’ at the bottom.
• The UN Number and Proper Shipping Name:g., “UN 1197, Extracts, Flavouring, Liquid.”
• Orientation Arrows:If containing liquid inner packagings, arrows indicating which way is “up” are mandatory.

Section 6: Exemptions and Exceptions: The “Limited Quantity” Rule

For the vaping industry, which often deals in smaller bottles of concentrates (e.g., 30ml, 120ml, 500ml), full regulation hazmat shipping can be prohibitively expensive and complex. Fortunately, regulatory bodies provide relief for smaller shipments through “Limited Quantity” (LQ) exceptions.

Shipping under Limited Quantity rules provides significant benefits: it often eliminates the need for UN-specification outer packaging (though sturdy packaging is still required) and, crucially, often removes the requirement for expensive Dangerous Goods Declaration (DGD) paperwork and certain carrier surcharges.

6.1 How Limited Quantity Works for Class 3

The applicability of LQ depends entirely on the Packing Group:

• For Packing Group II:The maximum inner packaging (the individual bottle) generally cannot exceed 1 Liter. The total gross weight of the completed package usually cannot exceed 30 kg (66 lbs).
• For Packing Group III:The maximum inner packaging generally cannot exceed 5 Liters. The total package weight limit remains 30 kg.

Limited Quantity Shipping Mark

6.2 The Catch with LQ

If you exceed these inner limits—for example, shipping a single 5-liter jug of a PG II concentrate—you cannot use Limited Quantity provisions. You must ship it as fully regulated dangerous goods with full UN packaging and paperwork.

Furthermore, air transport (IATA) has much stricter rules for LQ than road or sea. Some airlines may refuse LQ shipments entirely, or require different labeling (the ‘Y’ limited quantity mark).

CITATION 3: The Pipeline and Hazardous Materials Safety Administration (PHMSA), under the U.S. Department of Transportation, provides detailed guidance on Limited Quantity exceptions within 49 CFR Part 173.150. Information available at: https://www.phmsa.dot.gov/

Section 7: Best Practices for Flavor Concentrate Buyers

As a manufacturer of e-liquids buying concentrates, you are part of the chain of responsibility. Here is how you can ensure safety and compliance upon receipt and subsequent handling:

1. Demand Current SDS:Never accept a new flavor concentrate without a corresponding, recent SDS. Verify Section 14 immediately.
2. Inspect Incoming Shipments:When a flammable shipment arrives, check the condition of the boxes. Are the hazard labels visible? Is there evidence of leakage? Damaged hazmat packages should be rejected or handled with extreme caution by trained personnel.
3. Proper Storage:Flammable concentrates should not be stored next to heat sources, electrical panels, or oxidizers. Flammable liquid storage cabinets may be required depending on the total volume stored in your facility, dictated by local fire codes (e.g., NFPA 30 in the US).
4. Training:Ensure your warehouse staff is trained under relevant regulations (like DOT 49 CFR 172.704 in the US) to recognize hazmat markings and understand emergency response procedures in case of a spill.

Section 8: The Consequences of Non-Compliance

The rules surrounding flash point and shipping aren’t merely bureaucratic hoops; they are written in response to historical disasters. Ignoring them carries severe consequences.

• Safety Risks:The most critical risk is fire aboard an aircraft or seagoing vessel. A hidden flammable liquid leaking in a cargo hold can easily be ignited by friction or electrical faults. The resulting fire can be uncontrollable in transit, leading to catastrophic loss of life and assets.

CITATION 4: The National Fire Protection Association (NFPA) is a leading global advocate for fire and electrical safety. Their codes and standards, such as NFPA 30 (Flammable and Combustible Liquids Code), highlight the severe risks and necessary precautions for handling these materials. Source: https://www.nfpa.org/

• Financial and Legal Penalties:Regulatory bodies like the FAA (Federal Aviation Administration) in the US actively inspect cargo. The penalties for shipping undeclared or improperly packaged dangerous goods are astronomical. Civil penalties can reach tens of thousands of dollars per violation per day. In egregious cases involving willful negligence resulting in an incident, criminal charges and jail time are real possibilities for corporate officers.
• Operational Disruption:If a carrier suspects a shipment contains undeclared hazardous materials, they will ground it indefinitely. Your supply chain stops. You face storage fees, disposal fees for the seized goods, and the immense reputational damage of being labeled a high-risk shipper by major logistics carriers.

Conclusion: Precision in Chemistry, Precision in Logistics

In the world of flavor concentrate manufacturing, creating a stellar flavor profile is only half the battle. Ensuring that product reaches its destination safely and legally is equally vital.

Flash point is the critical pivot point around which the entire logistics strategy for a flavor concentrate revolves. It dictates the packaging you use, the labels you apply, the carriers you can utilize, and the costs you will incur.

By understanding the science of flash point, respecting the hierarchy of international regulations, and utilizing provisions like Limited Quantity intelligently, manufacturers can navigate the complexities of hazmat shipping. At our company, we view compliance not as a burden, but as an integral part of our quality promise—ensuring that the intense aromas we create inspire e-liquid makers around the world without compromising safety along the journey.

Loading Flammable Liquids for Global Transport

Call to Action

Are you navigating the complexities of formulating or importing flavor concentrates and need technical clarity on flash points and shipping regulations? Do you need access to a library of high-quality flavor concentrates that come with precise, compliant Safety Data Sheets every time?

Contact our technical team today. We can help you select the right flavor profiles that meet both your sensory goals and your logistical requirements. Let’s ensure your supply chain remains safe, compliant, and efficient.

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