Do shipping containers meet fire resistance?
What is fire resistance of shipping containers?
Fire resistance of shipping containers is a complex technical topic defining the ability of the container construction to withstand the effects of fire for a specified time without loss of key functions – primarily load‑bearing capacity, integrity and insulation capability. In the context of construction and alternative use of containers this question is crucial, especially because standard maritime ISO containers were not created with fire resistance in mind according to building codes.
Key facts:
- Standard shipping containers are not designed for fire resistance according to building regulations.
- There is no standardized documentation or certification of fire resistance for them.
- Construction from corten steel is non‑combustible (class A1), but at high temperatures it quickly loses strength.
- Floors made of plywood and some coatings are combustible.
- For building use the container must be professionally modified and fire safety must be documented.
Article contents
- Definition of key terms
- Properties of a standard shipping container in relation to fire
- Risks of an unmodified container in a fire
- How to achieve fire resistance in container buildings such as shipping container homes
- Legislative framework and standards in the Czech Republic
- Versatility of containers and safety responsibility
- Frequently asked questions (FAQ)
- Conclusion
Definition of key terms
| Term | Meaning |
|---|---|
| Fire resistance | Ability of the whole building construction (e.g., walls, ceiling) to withstand fire for a certain period (15–120 min). Assessed by criteria: R (load‑bearing), E (integrity), I (insulation). |
| Reaction to fire | Indicates how a material contributes to fire development. Highest class A1 (steel, concrete), lowest F (highly combustible). |
| Fire‑proofness | Lay term, technically inaccurate. Refers to non‑combustibility of a material but does not address the behavior of the whole construction in fire. |
| Maritime ISO container | Standardised transport unit made of corten steel, designed primarily for logistics, not for construction. |
| Construction (habitable) container | Modular unit intended for buildings (housing, offices), complying with construction and fire‑safety standards, with a declaration of conformity. |
Additional information from professional sources:
- Steel (class A1) does not burn, but above 500 °C its strength and ductility drop sharply.
- Wooden floors (usually plywood, ~28 mm) are a common weak point – reaction‑to‑fire class D or worse.
- Interior and exterior coatings may be based on organic resins that release toxic gases when burned.
Properties of a standard shipping container in relation to fire
| Property | Description and impact on fire resistance |
|---|---|
| Corten steel construction | High strength and weather resistance. In fire, strength dramatically decreases already at 500–600 °C, causing loss of load‑bearing capacity and stability. |
| Thermal conductivity of steel | Steel conducts heat quickly, leading to rapid transfer of high temperatures inside the container and to its structure. |
| Combustible components | Plywood floor (reaction‑to‑fire class D), organic paints, possible foam seals or insulation (PUR, EPS) can pose significant risk. |
| Hermetic sealing | Airtightness is advantageous for transport but increases the risk of pressure explosions in fire. |
Expert comment:
- The structural composition often combines external steel sheets, internal boards (drywall, chipboard) and an insulating core (glass or stone wool).
- When combustible internal claddings (chipboard, OSB) are used, wall fire resistance can drop to 15–30 min (national classification DP3).
- For higher fire‑resistance levels (e.g., REI 60, REI 90) certified non‑combustible materials and specialised assemblies are required.
Why is an unmodified container risky in a fire?
The combination of the above properties creates several unique hazards.
Pressure‑cooker effect (BLEVE, backdraft, flashover)
- Closed space with limited oxygen supply: The fire consumes oxygen, leading to incomplete combustion and the formation of flammable gases.
- Rapid temperature and pressure rise: Heat accumulates, internal pressure increases. Steel walls become extremely hot and pressure can exceed the structural capacity.
- Structural failure: At critical temperature (~600 °C) steel deforms and loses load‑bearing capacity.
- Explosive rupture (BLEVE/backdraft): When the structure gives way (e.g., doors open), accumulated gases explode, posing a severe danger to firefighters and the surroundings.
Real‑world examples:
- Tragic accident in Canada (Enderby, 2011), where a container fire led to an explosion with fatal consequences for the responding firefighter.
Additional risks:
- Storing flammable materials in an unmodified container is extremely hazardous because of the airtightness and BLEVE/flashover risk.
- Fire spread via wooden floors, paints and possibly foam insulation.
How to achieve fire resistance in container buildings
If a container is to be part of a building (for example shipping container home, container house), comprehensive modifications are required to reach the desired fire resistance (e.g., REI 60, REI 90).
Main principles and methods:
Passive fire protection:
- Interior claddings: Install certified fire‑resistant boards (e.g., gypsum GKF/DF, fibre‑cement Fermacell Firepanel A1, CETRIS). Number of layers and thickness determine the resulting resistance (e.g., 2–3 layers for REI 60–90).
- Thermal insulation: Non‑combustible mineral wool (glass or basalt), class A1 according to ČSN EN 13501‑1. Avoid foam insulations (PUR, EPS, PIR) which are combustible and release toxic gases.
- Exterior claddings: For buildings requiring external protection, use cement‑board, magnesite board or other non‑combustible panels.
- Fire‑retardant coatings: Intumescent paints slow steel heating, forming a foamy insulating layer (e.g., Promat, Nullifire, Hensel).
Structural modifications:
- Openings (windows, doors, ventilation): Reduce hermeticity and thus BLEVE risk; must use certified fire‑resistant products.
- Escape routes: Design must comply with ČSN 73 0802/0804 (PBŘ) – sufficient number and width of protected escape routes, minimum door width, etc.
- Joining multiple containers: Every joint and penetration must be treated as a potential fire barrier.
Active fire protection:
- Fire detectors: Autonomous or system smoke and heat detectors.
- Fire extinguishers: Must be present in sufficient capacity according to the standard.
- Automatic fire‑extinguishing systems: For larger objects or warehouses, installation of sprinklers or gas systems is possible.
Expert recommendation:
- The highest fire resistance is achieved with a sandwich: external steel sheet, A1 mineral wool, and 2–3 interior layers of fire‑resistant boards (Firepanel A1 or GKF).
- For storing hazardous substances use special containers with ventilation, a containment tray and fire‑resistant doors.
Legislative framework and standards in the Czech Republic
| Regulation/Standard | Significance for fire safety |
|---|---|
| Building Act (Act No. 283/2021 Sb.) | Defines a building, obliges a building permit or notification. |
| Decree No. 23/2008 Sb. | Technical conditions for fire protection of buildings, duties of the fire safety authority (PBŘ). |
| ČSN series 73 08xx | Code standards for fire safety of buildings – specific requirements for PBŘ, escape routes, structural resistance, storage, etc. |
| ČSN EN 13501‑2 | Method of classifying fire resistance of building components. |
| ČSN EN 1365‑1 | Test procedures for walls, ceilings, roof structures, etc. |
How to document fire resistance of container constructions?
- Testing: Performed in an accredited laboratory according to EN 1365‑1.
- Classification protocol: Manufacturer or system supplier provides a certificate (e.g., Fermacell Firepanel, Rigips GKF).
- PBŘ (Fire Safety Solution): Prepared by an authorised person (fire‑safety designer), mandatory part of the documentation for a building permit.
Versatility of containers and safety responsibility
Shipping containers are popular because of easy availability, robustness and modular construction:
- Uses: Warehouses, technical facilities, temporary or permanent buildings, shipping container homes, residential and office modules.
- Availability: Many companies offer thousands of units in stock, often in 20‑ and 40‑foot sizes, with free transport options.
- Safety responsibility: While ISO certification is sufficient for logistics, construction use requires active compliance with all legislative and safety requirements (PBŘ, structural calculations, hygiene, electrical inspection).
Recommendations:
- Every project using containers as a building should be designed, executed and inspected by professionals with a focus on fire safety.
- Investment in proper modifications is essential not only for legal compliance but also for the safety of people and protection of property.
Frequently Asked Questions (FAQ)
| Question | Answer |
|---|---|
| Is a shipping container combustible? | The steel structure is non‑combustible (A1), but the wooden floor, paints and contents can burn. |
| What is the fire resistance of an unmodified container? | Practically zero (REI 0) – it does not meet building requirements. In fire the structure quickly loses load‑bearing capacity. |
| Is a fire‑safety solution (PBŘ) required for a container house? | Yes, a PBŘ prepared by an authorised person is a mandatory part of the project documentation. |
| Can I safely store flammable materials in a container? | No, without special modifications (ventilation, containment tray, fire‑rated doors) it is extremely risky. |
Czech Republic, Trutnov 
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