Cellulosic vs Hydrocarbon Fire: Understanding the Different Protection Requirements

Cellulosic and hydrocarbon fires create different thermal exposures and protection requirements. Understand the fire curves, test standards and implications for passive fire protection.

Fire protection is not specified simply by asking how many hours a material or assembly can resist fire.

The type of fire exposure matters.

A structural element exposed to a conventional building fire does not experience the same thermal conditions as equipment or structural steel exposed to a hydrocarbon fire in an oil and gas facility. The rate at which temperatures rise, the severity of the exposure and the duration of the thermal load can all influence the protection strategy.

For engineers, designers and specifiers, understanding this distinction is important because a fire-resistance rating only has meaning when considered in relation to the fire exposure, test method, protected element and performance criteria against which it was established.

Two commonly encountered fire exposure scenarios are cellulosic fires and hydrocarbon fires.

What is a cellulosic fire?

A cellulosic fire represents a fire involving ordinary combustible materials commonly found in buildings and infrastructure, such as wood, paper, textiles and other materials containing cellulose.

The standardised fire exposure used for many building fire-resistance tests is represented by a time-temperature curve. ISO 834-1:2025 specifies fire-resistance test methods using standardised time-temperature curves to assess the performance of construction elements under defined fire exposure conditions.

The important point is that this is a standardised test exposure, rather than a prediction of the exact temperature that will occur in every real building fire.

The temperature increases progressively with time, providing a repeatable basis for testing walls, floors, doors and other construction elements.

This allows different assemblies to be assessed against consistent fire-resistance criteria.

What is a hydrocarbon fire?

Hydrocarbon fires arise from the combustion of fuels such as crude oil, petroleum products, natural gas and other hydrocarbons.

They are particularly relevant to facilities where flammable liquids or gases are processed, stored or transported, including:

• Refineries
• Petrochemical plants
• Oil and gas processing facilities
• LNG and gas facilities
• Fuel terminals
• Offshore installations
• Certain industrial process facilities

The thermal exposure associated with hydrocarbon fire scenarios can develop much more rapidly than the standard cellulosic fire exposure.

This rapid temperature rise is one of the reasons hydrocarbon fire protection requires specific testing and qualification rather than simply relying on a conventional building fire-resistance rating.

UL 1709, for example, is specifically titled the Standard for Rapid Rise Fire Tests of Protection Materials for Structural Steel and is commonly associated with hydrocarbon-type fire exposure.

The key difference: how the fire develops

The distinction becomes clearer when the two fire scenarios are considered as thermal exposure profiles.

Cellulosic fire

A conventional cellulosic fire curve represents a progressively increasing temperature exposure.

The curve is intended to provide a standardised basis for evaluating fire resistance over time.

Hydrocarbon fire

A hydrocarbon-type fire represents a rapid-rise thermal exposure associated with burning hydrocarbon fuels.

For protection systems used in high-hazard industrial environments, the early development of the fire can therefore be particularly significant.

This difference affects how quickly an unprotected steel element, for example, can absorb heat and approach temperatures at which its structural properties are significantly affected.

The important engineering principle is therefore:

Fire resistance cannot be separated from the fire exposure against which the system has been tested.

A protection system tested under one fire exposure should not automatically be assumed to provide equivalent performance under another.

Why does the difference matter for structural steel?

Steel does not need to melt before fire becomes a structural concern.

As its temperature increases, the mechanical properties of structural steel change. Strength and stiffness reduce, and the capacity of an unprotected member can therefore deteriorate significantly during a severe fire.

Passive fire protection is used to delay the rate at which the steel heats up, providing additional time before critical temperatures are reached.

The required protection therefore depends on factors including:

• The design fire scenario
• Required fire duration
• Steel section geometry
• Section factor
• Applied loads
• Critical steel temperature
• Protection material properties
• Protection thickness
• Exposure conditions
• Testing and assessment methodology

This is why simply specifying “2-hour fire protection” without defining the applicable fire exposure can be technically incomplete.

Fire resistance is not a universal property

A common misconception is that a product described as “2-hour fire rated” will provide the same protection under any fire condition.

It does not necessarily follow.

Fire-resistance performance is established through a particular test or assessment methodology, involving a defined specimen, substrate, installation arrangement, exposure and performance criteria.

ISO 834-1:2025 describes fire-resistance testing using standardised time-temperature curves and establishes the basis for evaluating construction elements under those defined exposure conditions.

Similarly, UL 1709 addresses rapid-rise fire exposure for protection materials used on structural steel. UL Solutions notes that certification to this standard is particularly relevant when evaluating protection for high-risk environments such as petrochemical facilities.

The result is that two systems carrying similar nominal fire durations may have been evaluated against different fire exposures and different test methodologies.

For specification purposes, the test standard is therefore as important as the stated duration.

Cellulosic and hydrocarbon fires: a practical comparison

Typical Application

Cellulosic fire: Buildings and conventional infrastructure.

Hydrocarbon fire: Oil, gas and petrochemical facilities.

Primary Fuel Type

Cellulosic fire: Cellulose-based combustibles and other ordinary contents.

Hydrocarbon fire: Hydrocarbon fuels.

Thermal Development

Cellulosic fire: Progressive standardised temperature rise.

Hydrocarbon fire: Rapid temperature rise.

Typical Protection Context

Cellulosic fire: Walls, floors, doors, structural elements and building assemblies.

Hydrocarbon fire: Structural steel, process structures and industrial equipment.

Relevant Testing

Cellulosic fire: ISO 834-based fire-resistance testing and related standards.

Hydrocarbon fire: UL 1709 and other hydrocarbon-specific test methods.

Key Specification Issue

Cellulosic fire: Required fire-resistance duration and performance criteria.

Hydrocarbon fire: Fire scenario, rapid thermal exposure and suitability of the protection system.

Protection Approach

Cellulosic fire: Depends on the element and required performance.

Hydrocarbon fire: Often requires protection specifically qualified for severe industrial fire exposure.

The above information should be treated as a high-level engineering comparison, not as a substitute for the applicable project standard or fire engineering assessment.

Hydrocarbon fire does not mean one single fire scenario

There is another distinction that is important in industrial fire protection.

“Hydrocarbon fire” is not necessarily one universal exposure condition.

For example, a pool fire and a jet fire represent different physical scenarios.

A pool fire can occur when a flammable liquid accumulates and burns over a surface.

A jet fire can occur when a pressurized flammable fluid is released and ignites, producing a high-velocity flame.

These scenarios can impose different thermal and mechanical demands on passive fire protection.

API RP 2218, Fireproofing Practices in Petroleum and Petrochemical Processing Plants, focuses specifically on fireproofing practices for pool-fire scenarios in petroleum and petrochemical processing plants. It also contains information relating to jet-fire considerations, while making clear that its primary scope is passive fireproofing for pool-fire scenarios.

For jet-fire resistance, ISO 22899-1:2021 provides a dedicated test method for determining the resistance of passive fire protection materials and systems to jet fires.

This distinction is important because a specification should begin with the credible fire scenario, rather than selecting a protection product first and assuming that its fire rating covers every condition.

What does this mean for passive fire protection?

Passive fire protection is generally intended to delay the effects of fire on the protected element rather than eliminate the fire itself.

In industrial facilities, this can be particularly important for structural supports and equipment whose continued stability or functionality may be necessary to support emergency response, isolation, shutdown or evacuation.

API RP 2218 describes fireproofing as a means of limiting property loss from pool fires and notes that properly implemented passive fireproofing can protect against intense and prolonged heat exposure that could otherwise contribute to equipment failure, escalation and property loss.

The objective is therefore not simply “make the steel fireproof.”

It is to provide a defined period of thermal protection appropriate to the credible fire scenario and the function of the protected asset.

What engineers should consider when selecting protection

Before specifying a fire protection system, several questions should be established.

1. What is the design fire?

Is the project concerned with:

• Cellulosic fire?
• Pool fire?
• Jet fire?
• A tunnel fire scenario?
• Another project-specific fire exposure?

The answer determines which test methods and performance data are relevant.

2. What is being protected?

A structural steel column, process support, wall, enclosure, equipment item and penetration do not necessarily have the same protection requirements.

3. What performance is required?

The requirement may relate to:

• Load-bearing capacity
• Integrity
• Insulation
• Temperature limitation
• Functional performance
• Fire compartmentation

These criteria should not be treated as interchangeable.

4. What standard or test method demonstrates the required performance?

The specification should identify the applicable standard and ensure that the product/system has been tested or assessed for the intended application.

5. Does the tested configuration match the proposed installation?

This is particularly important for passive fire protection.

Substrate, geometry, thickness, joints, fixings, penetrations, interfaces and installation conditions can all affect performance.

6. What happens after the fire?

For industrial assets, protection may also need to be considered alongside inspection, maintenance, corrosion exposure, mechanical damage and the ability to repair or reinstate the system.

The specification should start with the fire scenario

The most important takeaway is straightforward:

Fire protection should be selected against the fire exposure the asset is expected to withstand.

A cellulosic fire test does not automatically demonstrate hydrocarbon-fire performance. Likewise, a hydrocarbon qualification should not automatically be interpreted as demonstrating every other form of fire resistance.

For engineers and specifiers, the correct sequence is therefore:

Define the credible fire scenario → establish the required performance → identify the applicable test/assessment standard → select a qualified protection system → verify the installation configuration.

This approach provides a much stronger technical basis for passive fire protection than specifying a fire-resistance duration alone.

Key takeaways

Cellulosic and hydrocarbon fires represent different thermal exposure conditions.

Hydrocarbon fires are associated with rapid temperature rise and severe thermal exposure.

Fire-resistance duration should always be considered alongside the fire exposure and test method.

Pool-fire and jet-fire scenarios should not automatically be treated as equivalent.

UL 1709 is a key rapid-rise fire test for protection materials used on structural steel.

ISO 22899-1 provides a dedicated method for evaluating passive fire protection under jet-fire exposure.

API RP 2218 provides guidance on passive fireproofing practices in petroleum and petrochemical processing plants, with a focus on pool-fire scenarios.

The suitability of a fire protection system depends on the specific application, exposure, substrate, configuration and required performance.

References

ISO 834-1:2025 — Fire-resistance tests — Elements of building construction — Part 1: General requirements. ISO.

UL 1709 — Standard for Rapid Rise Fire Tests of Protection Materials for Structural Steel. UL Solutions.

ISO 22899-1:2021 — Determination of the resistance to jet fires of passive fire protection materials — Part 1: General requirements. ISO.

API RP 2218 — Fireproofing Practices in Petroleum and Petrochemical Processing Plants. American Petroleum Institute.