Are Shipping Containers Fireproof?

Shipping containers are fire-resistant, not fireproof. While their steel construction won’t ignite, they’re far from invulnerable to fire. High temperatures can compromise structural integrity, conduct heat to contents inside, and any flammable materials within the container remain at risk.

In this guide, we’ll break down how shipping containers respond to fire, what their temperature thresholds are, and the fireproofing steps you can take to keep your container and its contents safe.

Are Shipping Container Materials Fireproof?

A standard shipping container is built from Corten steel, a marine-grade metal known for corrosion resistance and strength. As a non-combustible material, steel doesn’t ignite or support flames, providing a strong barrier against embers, radiant heat, and brief fire exposure.

While this makes steel an excellent first line of defense against fire, the material itself isn’t without vulnerabilities. Corten steel’s weaknesses include:

• High heat conductivity: It transfers heat quickly, making the interior dangerously hot even if flames are outside.
• Loss of structural strength: Steel begins to soften and deform under sustained high temperatures.

Other container components that are not fireproof

Shipping containers contain other components beyond Corten steel that are not fireproof.

• Flooring: Most containers have plywood floors, which are combustible and can burn readily.
• Seals & gaskets: Rubber seals can melt or ignite.
• Paint coatings: Standard container paint may blister or release fumes when exposed to high heat.

Fire-resistant vs. fireproof

Fire-resistant materials can withstand fire for a limited time or resist ignition, but will eventually succumb to prolonged heat exposure. Fireproof materials, by contrast, cannot burn under any circumstances.

Shipping containers are fire-resistant rather than fireproof. They offer strong protection against flames, but extended exposure will ultimately cause structural damage.

How Fire-Resistant Are Shipping Containers?

Shipping containers have limited fire resistance despite being made of steel. While they won’t easily catch fire like wood, they’re vulnerable to structural failure under intense heat.

Temperature thresholds for structural failure

Steel’s performance drops significantly as temperatures rise:

• 572°F (300°C): Steel begins to lose structural strength.
• 932–1112°F (500–600°C): Steel loses half its load-bearing capacity and may warp.
• 2,500°F (~1,370°C) : Steel approaches melting point.

A typical building or wildfire can reach temperatures of 1,112–1,832°F (600–1,000°C), enough to deform a container even if it doesn’t melt.

Fire ratings and certification standards

Shipping containers themselves are not built with fire ratings, but when converted into buildings, components must meet codes such as:

• ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials.
• UL 263: fire tests of building construction materials

Container conversions may require fire-rated walls, ceilings, and insulation to meet local building codes.

How Do Shipping Containers Perform in External Fire Situations?

Shipping containers offer some protection in external fire situations like nearby building fires, wildfires, or burning fuel sources. Their steel construction and enclosed design help shield contents from direct flames and flying embers.

However, the metal walls conduct heat, which can raise interior temperatures enough to damage or destroy sensitive items. Plywood floors and container doors are especially vulnerable to prolonged heat, and warping may make doors difficult or impossible to open.

Overall, shipping containers provide moderate fire resistance. In high-intensity or long-lasting fires, their protective benefits are limited, and contents may still be at risk. Therefore, containers should not be used as fire shelters.

How Do Internal Fires Behave Inside Shipping Containers?

Internal container fires behave very differently from external ones because the container becomes an enclosed environment. Once flames ignite inside, limited ventilation, trapped heat, and combustible cargo can create extreme conditions quickly.

Common Causes of Internal Container Fires

While shipping containers are often thought of as passive storage units, many fires actually start from within. Shipping containers frequently transport hazardous goods, and many fires originate from inside due to:

• Misdeclared lithium batteries
• Self-heating cargo like charcoal, fertilizers, or oil-soaked rags
• Chemical reactions and leaking substances
• Improperly stored fuels, solvents, or flammable goods

Fire Dynamics in Sealed Containers

Shipping containers are designed to be strong and relatively airtight, but this very characteristic significantly influences how fires behave inside.

Unlike open spaces, fires in sealed containers interact with limited oxygen, confined heat, and dense materials. This can cause it to behaviour differently:

• Fires may start aggressively but die down as oxygen depletes.
• Smoldering fires can continue for hours and reignite when oxygen enters (door opening effect).
• Heat can accumulate rapidly, creating oven-like conditions that damage everything inside.

This means that the structure of the container may survive longer, but not the contents.

Fire Risks in Modified Shipping Containers (Homes and Offices)

When shipping containers are converted into homes, offices, or other functional spaces, new fire risks emerge that aren’t present in standard storage units. While the steel shell provides structural strength, the addition of interior materials and utilities introduces additional fire considerations:

• Modifications and Added Materials: Wood framing, insulation, electrical systems, and furnishings added during conversion dramatically increase fire risk compared to bare steel.
• Interior Materials: Original wooden floors and interior paneling ignite quickly unless treated with fire retardants or replaced with fire-rated alternatives.
• Heat Transfer: Steel walls conduct heat rapidly throughout the structure, allowing interior temperatures to reach dangerous levels even without direct flame contact.
• Ventilation and Seals: Standard vents and seals create entry points for flames, embers, smoke, and heat when exposed to fire conditions.

Understanding these risks highlights the need for intentional fire prevention and fireproofing measures when using shipping containers as functional living spaces or even storages.

Fire Prevention and Fireproofing for Shipping Containers

Shipping containers inherently resist fire better than many other storage options thanks to their steel construction. However, steel alone does not prevent fires, and interior contents remain vulnerable to heat and flames. To maximize safety, a combination of prevention, fireproofing, and proper maintenance is essential.

Prevention vs. Fireproofing

Fire prevention focuses on reducing the risk of ignition, while fireproofing enhances the container’s ability to withstand flames, heat, and smoke. Both strategies are critical for protecting cargo and equipment.

Passive Fireproofing

Fireproofing materials are built into the container structure to slow fire spread and protect interior contents. These materials improve fire resistance:

• Fire-resistant boards such as cement board or gypsum board can line walls and ceilings to resist flames.
• Mineral wool insulation is non-combustible and provides thermal protection, reducing heat transfer to the container interior.
• Intumescent paint applied to steel expands when exposed to heat, forming an insulating layer that delays metal deformation.
• Non-combustible exterior cladding adds an additional barrier against external fire threats, particularly for converted containers used as offices or homes.

Active Fire Protection Systems

Active fire protection systems are designed to detect, control, or suppress fires as they occur, rather than simply resisting flames. The type and complexity of these systems depend on how the container is used and the risks involved.

• Smoke detectors & alarms: Early detection systems identify smoldering fires before they escalate. Interconnected alarms in modified containers ensure immediate occupant warning.
• Sprinklers or mist systems: Water-based systems control or extinguish fires quickly. Mist systems use fine droplets to absorb heat and displace oxygen, ideal for enclosed spaces with water-sensitive cargo.
• Chemical fire suppression: Server rooms, battery storage, and electronics require chemical systems that suppress flames without water damage, particularly for electrical or flammable liquid fires.

Safe Storage Practices

Proper storage practices are one of the most effective ways to prevent internal fires in shipping containers.

• Label and segregate flammable cargo: Mark and separate incompatible materials to prevent accidental ignition and chemical reactions.
• Keep lithium batteries in approved packaging: Use certified packaging to contain heat and prevent short-circuiting during transport.
• Avoid storing fuels or solvents without proper containment: Store in leak-proof, approved containers with adequate ventilation to prevent vapor ignition.
• Maintain clear documentation and hazard declarations: Keep accurate records of hazardous materials for regulatory compliance and emergency response.

By following these practices and understanding what not to store in a shipping container, you greatly reduce the risk of
internal fires and protect both the structure and its contents.

Maintenance Tips for Improving Fire Safety

Regular maintenance is essential to keep shipping containers safe from fire hazards. Even a structurally sound container can become a risk if seals, surfaces, or electrical systems are neglected. Key maintenance practices include:

• Inspect seals and door gaskets: Check regularly for cracks or degradation to maintain airtight protection against smoke and heat.
• Check for damaged paint or exposed metal: Touch up coatings to prevent rapid heat transfer and reduce warping risk during fires.
• Maintain ventilation systems: Keep vents and HVAC systems clean and unobstructed to prevent heat buildup.
• Remove accumulated debris, dust, or chemicals: Regular cleaning eliminates ignition sources like dust, paper, and chemical residue.
• Ensure electrical modifications meet code: Verify all wiring and installations comply with safety codes to prevent overheating and short circuits.

Shipping containers are fire-resistant, not fireproof. Steel construction resists flames but conducts heat rapidly and weakens under extreme temperatures. Interior contents remain vulnerable, and combustible components like plywood floors and modification materials increase fire risk.

Enhancing safety requires proper fireproofing measures. Fire-resistant insulation, protective coatings, suppression systems, and proper storage practices significantly improve protection. For conversions, meeting fire codes with regular maintenance ensures reliable performance.

Whether you need a container for storage, conversion, or transport, Viva Containers offers high-quality containers designed to withstand the toughest environments. Offering both new and used containers, including specialized options like high cubes, open sides, and double-door models. Take a look at our container listings online or get in touch for a personalized quote, and let Viva Containers be your reliable partner.