Fire safety and resistance of shipping containers
Fire safety and fire resistance of a shipping container is an interesting topic, one that many customers inquire about, especially those considering a shipping container as an alternative for housing, a cabin, a sales booth, etc.
In general, a shipping container is made as a “transport packaging” according to the rules for maritime, rail, and truck transport.
According to information from suppliers, there is no documentation for maritime ISO containers specifically regarding the fire safety of the shipping container. Neither factories nor inspection companies have issued such documentation. And as far as we know, this fire safety document for shipping containers is not issued as a standard document for transport containers.
Exceptions are construction cells, office containers, sanitary containers, etc. However, the rules here are different, and these containers must have a so-called “declaration of conformity.” However, this does not apply to maritime containers.
In principle, it can be said that maritime containers made of corten steel have a certain fire resistance, because steel, unlike wood, is an inorganic material and is itself non-flammable. However, steel has high thermal conductivity, and under the influence of heat, its internal structure changes, leading to a loss of load-bearing capacity and elasticity. The specific fire resistance, however, depends on various factors, including the type of construction, materials used, and the type/density of the coating.
But no one realizes that when a container with its specific properties is closed, as it is built for transport (i.e., with sealing doors, without windows, vents, etc.) and inside there is flammable material that somehow ignites (as happened in Enderby, for example), the container’s resistance and strength could (although unintentionally) create an unimaginable problem in case of fire. A closed and strong-sealing container will behave completely differently in the case of an internal fire compared to a wooden cabin… and this is something to think about first and foremost.
Always think about fire safety!
This article has been written to inform the general public.
How to explain the term “Fire Resistance?”
Fire resistance is a similar term that often describes a material’s ability to withstand high temperatures without melting or significantly damaging. Steel containers are fire-resistant in this sense, but not indestructible.
Fire resistance refers to the overall ability of the container to resist fire, including the construction, material, and design. Although maritime containers are resistant, they are not completely fireproof and may be damaged by prolonged exposure to intense heat.
Fire protection and safety of maritime containers include measures that minimize the risk of fire and prevent its spread. This can be achieved by using non-flammable materials, construction, placement of containers, and safety protocols.
All the information in this article is for informational purposes only. We have drawn heavily from the internet, where we also found this quite interesting article, see below: Article source: Fire Chiefs’ Association of BC | www.fcabc.ca
Conclusion: This material is not intended to create panic. It is an informative article whose purpose is for anyone who uses a container for purposes other than those for which it is primarily intended to always consider fire safety. This means that in the case of a conversion, etc., they must comply with provisions and regulations. They should ensure an electrical installation review, make necessary modifications to the container (such as weakening the structure – by adding windows, doors, vents, etc.) in case of fire inside, and store the materials properly.
Fire safety needs to be kept in mind…
What happened in the past?
The death of Captain Daniel Botkin, a volunteer firefighter in Enderby, in 2011, which occurred while performing his duties, served as a warning for firefighters about the fire hazards of shipping containers.
It was discovered that exposing a shipping container to fire and the presence of a small volume of flammable liquids led to an internal explosion at low speed, which blew the doors off the container. One of these doors subsequently struck Captain Botkin, who died at the scene.
In April 2013, a leaking grill tank exploded inside a shipping container in Saanich, destroying the entire container. Pieces of the container were found as far as 274 meters away, and the walls were leveled. Fortunately, no one was seriously injured during this event.
To prevent similar injuries to the public and firefighters, fire safety requires the following actions:
• Informing about the fire safety hazards of shipping containers
• Safe use of shipping containers as temporary buildings or permanent residences
• Regulating materials stored in shipping containers
• Providing information and guidelines on how shipping containers can be modified to be safer
• Providing procedures that the fire service can use to address fires in shipping container buildings
This article provides information and recommendations on how to improve fire safety in shipping containers.
General information about shipping containers
Over 16 million shipping containers are used to transport goods and materials by sea, rail, and truck. Millions of these containers become surplus each year and are repurposed into buildings or structures for other uses.
These surplus containers are made of steel and range in size from 1.5 meters to 16 meters (5 to 53 feet in length). Standard containers are 2.4 meters (8 feet) wide and 2.6 meters (8.5 feet) high, with steel doors on one or more sides.
Some shipping containers have small vents on their ends at the top, called vent grills, to balance air pressure changes due to surrounding air temperature (±20 to 30°C).
These vent grills are holes through the steel wall and are covered with a metal or plastic outer casing. The grills have 2, 4, or 6 sets of these grills, depending on the size of the container.
Standard containers are designed to be stackable to a height of 6 to 9 containers and can support a weight of 32,205 kg. The side walls are designed to withstand sliding loads up to 60% of the allowable load. The front walls and doors are designed to withstand 40% of the allowable load.
As a result, these containers are capable of withstanding internal pressure increases to the point where catastrophic failure occurs.
The properties of shipping containers that make them secure against theft and structurally strong also make them a fire safety risk until they are regulated, weakened, and handled carefully during a fire.
Summary of the Enderby Lodd Incident
On December 29, 2011, at 3:51 a.m., a fire was reported to 911 at a construction site for wood-frame buildings in Enderby, BC.
At 4:01 a.m., the first fire truck arrived with 15 firefighters (including the deputy fire chief and 4 fire captains), along with two pumps and a rescue vehicle. The fire likely started in a modular trailer and spread to a large production hall. It was a building where log constructions were being assembled.
The fire in the production building revealed a 2.4 meter wide, 2.6 meter high, and 12 meter long shipping container located under a roofed extension of the production building, about 2 meters from the building. During the fire, smoke appeared several times from the vents and from overheated door seals. Water was directed onto the container or its surface.
At approximately 5:05 a.m., the fire captain climbed onto the roof of the container to fight the fire in the production building. While the captain was on top of the container, it was not hot.
The incident commander was concerned about the potential failure of the production building’s structure and moved the firefighters away from the structure and the shipping container. The operation transitioned into the mop-up phase.
Ignorance led to a fatal mistake
At 05:15, the transport container exploded and:
- one of the sides of the transport container along the roof line tore along its entire length
- the roof along the production building was bent upwards
- the walls of the container and ends were bent outward
- both metal doors weighing 113kg were blown off
One door struck Fire Captain Botkin and landed 41 meters southwest of the container. The other door was found 54 meters northwest of the container. Fire Captain Botkin died at the scene.
Fire safety compliance is essential!
Various investigation reports suggest that the explosion was caused by 1/2 liter to 1.5 liters of gasoline/oil from two chainsaws and 1/2 liter of methyl hydrate. Witnesses reported that the fire had been affecting the transport container for 45 to 55 minutes before the explosion. One of the fire commanders was on the roof of the transport container 10 minutes before the explosion, directing a hose at the fire in the production building. At that time, Fire Captain Botkin did not find the top of the steel structure warm.
Awareness of Danger and Regulations – Fire Safety
Transport containers are not considered a safety risk when used to transport various goods and materials, including hazardous goods on roads, railways, and ships. However, when used as buildings or structures, they are not associated with fire safety risks. The incidents in Enderby and Saanich are two examples of fire safety risks they can create.
Examples of risks can be found where transport containers are used for:
- storage of fireworks,
- storage of flammable gases and liquids at construction sites,
- as first aid buildings on construction sites (with supplies of antiseptic alcohol or oxygen bottles),
- used as construction offices,
- used by hobbyists to recharge hunting ammunition,
- used as electrical rooms or electrical cabinets at construction sites (with the accompanying risk of electrical arc explosion),
- Possibilities of use are limited only by the user’s imagination…
The main reason transport containers are used as temporary or permanent structures is their low acquisition cost. They do not require assembly, are weather-resistant, structurally solid, are closed containers, and are secured against theft.
These containers are also not viewed as buildings or structures, and therefore do not meet the requirements for building and fire permits. Many states and cities in the United States have implemented regulations for planning or construction that govern the use of these containers.
In order to regulate the fire safety of transport containers, specific legal procedures and steps should be introduced by each state. This is to prevent similar events, often due to ignorance.
Prevention – How to Prevent Similar Events that Happened…
The key elements of fire mitigation strategies in ships and ensuring fire safety in containers are:
REGULATION AND APPROPRIATE USE
As mentioned above, it is crucial to regulate what transport containers are used for, what contents can be safely stored in transport containers, and whether there is any potential fire risk that transport containers are exposed to or could create for critical structures or access points at construction sites.
WEAKENING CONSTRUCTION FOR FIRE SAFETY
Weaken the transport containers to prevent the build-up of high pressure inside the containers, which could exceed the container’s strength during rupture. Current standard transport containers have a very strong construction to withstand the load and forces during stacking, twisting, and dropping on ships, trucks, and trains.
These containers are also designed to be strong to prevent theft of their contents. Containers can be weakened by installing anti-blast panels that may cover more than 25% of the wall area, replacing the end doors with lightweight walls, installing standard doors and windows on the sides… The degree to which a container must be weakened depends on the specific use of the container. If hazardous goods are to be stored in the containers, specially designed relief panels must be determined by a professional engineer. Small upper and lower ventilation holes can be used to provide some weakening of containers at a low level and to ensure ventilation inside the container.
VENTILATION OF THE SHIPPING CONTAINER
Lack of clues about what is happening inside the transport container was one of the key issues in the Enderby incident. The firefighters were not fully aware that the interior of the transport container was expanding. Ensuring openings at the top and bottom of the container at opposite ends could have indicated that smoke was being pushed out of the container and that dangerous conditions were developing inside the container. This information could have allowed them to change tactics.
FIRE SAFETY
Fire brigades should consider introducing standard operating procedures related to determining the size of the event, hot and excluded zones, and planning the fire attack. In subsequent articles, we will provide a framework for a typical standard operating procedure for fires in maritime containers.
Related articles we are preparing for you in connection with this topic: How to proceed in the event of a fire in shipping containers, Minimum standards for using shipping containers as storage buildings
Analysis of Events in Enderby
Reports from WorksafeBC and the Office of the Fire Commissioner identified specific fuels that could have been part of the Enderby incident, but they had trouble identifying the ignition scenario. An NFPA advisor helped conclude that there was a “low-volume detonation”.
SITUATION RESEARCH
Some information is available on the ISO design standards for shipping containers used for their original purpose of transporting goods and materials. These standards change depending on the operating conditions of the containers. Older containers had fewer ventilation holes for air compensation compared to newer containers, and the range of container sizes has also increased.
The only document found about fire tests on shipping containers is the U.S. Coast Guard report from 1977 “Fire Performance of Intermodal Shipping Containers”. This testing examined the consequences of fires inside containers and fires caused by exposure that impacted shipping containers. Internal testing included a wooden cradle fire inside the container, which either glazed over or consumed the internal oxygen before all the wood could burn.
Air compensating vents had no effect on the test results. The second exposure tests involved 65m2 spilled JP5 fires, where individual and stacked containers were exposed. These tests showed that internal temperatures reached 230°C within 4 to 9 minutes. The conclusion was that there is a possibility of “ignition or charring” of Class A materials within 5 minutes.
FUELS
It was generally concluded that it involved 500 milliliters of methyl hydrate (methanol) or approximately one liter of gasoline, or a combination of both fuels. The following tables show some information about the properties of methanol and gasoline and, for comparison, also propane and hydrogen:
Some key information from this table is that when heated, methanol vapors can rise, and gasoline vapors remain low. The autoignition temperature (AIT) of methanol is significantly higher than that of gasoline. The flammability ranges are similar, and the combustion energy of gasoline is significantly higher than that of methanol.
The temperature at the top of the shipping container will also be higher than at the floor, resulting in a lower minimum ignition energy. For example, the minimum ignition energy (MIE) of ethanol at 250°C is 0.40 mJ, but at 100°C, the MIE is 0.21 mJ. If the pressure in the container increases, the AIT also decreases.
IGNITION SOURCES
The ignition source is the most difficult to determine. Although there was information that the side of the manufacturing building of the shipping container was exposed to direct flame, which could have heated the steel above the ignition temperature of the fuels, one of the fire watch commanders was on the roof of the shipping container 10 minutes before the explosion and stated that the roof was not hot. A key temperature indicator in the report is that two chainsaws were hanging on the side wall of the manufacturing building of the shipping container and that plastic gas tanks had melted. The chainsaw manufacturer informed WorksafeBC that the melting temperature of the chainsaw plastic is approximately 200°C. This would mean that spilled or evaporated gasoline was exposed to a temperature of at least 200°C, and the AIT of gasoline is 232°C.
Exposure tests conducted by the U.S. Coast Guard showed that the temperature at the ceiling of the container at 2 meters was approximately 360°C within 6 minutes of the start of the test fire. Witnesses stated that flames were licking the side of the container for 45 to 55 minutes. Based on fire tests, it was concluded that the temperature in the area where the chainsaws (and gasoline was leaking from them) were located could have been at least 200°C or significantly higher. It would then be possible to theorize that this area inside the container was heated by radiation, conduction, and convection to a temperature higher than the autoignition temperature of gasoline and possibly methanol.
CONTAINER CHARACTERISTICS
U.S. Coast Guard fire tests provide some basic information on the fire characteristics of shipping containers; however, they do not provide any crucial information on strength and ventilation. Based on published information on wall loading, a conservative estimate of wall strength was made, and these calculations determined that the yield strength of the walls would be 7.0 kPa (1.0 psi) and the tensile strength 8.4 kPa (1.22 psi). This value is lower than the rough estimate but is useful for determining the area of explosion panels.
Air compensating vents are designed to balance climatic temperature changes without damaging the container. If they were not installed, small temperature changes could dramatically increase the internal pressure within the container. Using the ideal gas law and assuming the container was not ventilated, the following pressure increase could occur:
These ventilation holes are unable to release enough pressure quickly enough during a fire because they only make up 0.0079% of the area of the walls and roof of a typical shipping container.
VENTILATION SCENARIOS
To prevent the rupture of the shipping container and similar incidents as in Enderby with similar fuels, calculations were performed in accordance with NFPA 68-2012. The following table shows the required venting area for explosion venting for different fuels for standard 12m long containers:
These venting areas are only for comparison, as the key factor in calculating the container’s strength is only a rough estimate.
The key conclusion is that even very small unregulated volumes of flammable liquids or gases in shipping containers can cause an explosion with low energy and rupture the shipping container.
CONCLUSION – FIRE SAFETY
To prevent injury to the public and firefighters, we must work on:
- informing about the fire safety risks of shipping containers,
- implementing national, provincial, and local government regulations for the use of shipping containers as temporary buildings and structures,
- regulating materials stored in shipping containers,
- providing information on how shipping containers can be modified to be safer
- providing operational procedures that firefighters can use to safely address fires in shipping containers