Evaluating performance of fire-rated floor and access doors

by arslan_ahmed | March 1, 2024 7:20 pm

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By Steve Weyel

Building owners know fire can destroy a building in minutes. They are also aware that active and passive fire protection equipment play important roles in keeping the structure and its occupants safe.

What is not as well-known is how fire-rated floor doors play an essential role in passive fire protection. Building codes classify two types of doors for fire-rated openings in horizontal assemblies: fire-rated floor doors and fire-rated access doors. Each of these door types meet specific fire protection requirements for the applications in which they are intended. Fire-rated floor doors have a fire resistance rating. Fire-rated access doors have a more stringent fire protective rating.

Doors with fire protective rating address heat transfer and include intumescent coatings. Both are important to understand for specifiers and how they factor into design.

Heat transfer

When a fire erupts, everyone can see flames and the inherent danger they represent. What is less well-known, however, is how the fire started. This is especially important to recognize in buildings, where concealed spaces house wiring and other materials that could trigger a blaze.

For fire to occur, three components—heat, fuel, and oxygen—are needed to ignite and sustain it. All these elements in the “fire triangle” are required. If one is removed, the fire will be extinguished. A fire starts when all three elements are present in the right proportions and danger develops when fire spreads. Heat from fire transfers through convection, conduction, radiation, or direct burning. For commercial property owners, convection and conduction fires are of particular importance.

Most fire protection experts report convection fires are most common in domestic and commercial buildings. Fire causes the air around it to heat and produces smoke. Warm air rises, but the heat is trapped when it hits a ceiling and begins to travel horizontally. As the fire spreads, combustible materials will also ignite and fuel the fire.

Conduction fires spread when materials contact each other. Heat energy is transmitted through collisions between atoms and molecules. It occurs more readily in solids and liquids, and the rate of energy transfer is higher when there is a large temperature difference between materials that are in contact.

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Metal is a good conductor of heat. Diamond is the leading thermally conductive material—hardly a concern for owners of commercial buildings—but silver and copper are also highly conductive. Silver has a 429 W/m•K, which is a unit of measurement for thermal conductivity, and is a component of many appliances. Copper (398 W/m•K) is commonly used for manufacturing conductive appliances. Hot water pipes are among the products that use the conductive properties of copper. Concrete and brick have low thermal conductivity, as does insulation.

Heat transfer can also occur through radiation. Heat is transferred through the air due to electromagnetic waves. Heat spreads in multiple directions until it connects with an absorbent object. Through radiation, a fire can spread through windows, lighting materials on fire and causing a quick spread that can destroy other buildings.

Intumescent coatings

Intumescent coatings, or paint, is applied to structural elements and prevents objects from losing their strength in a fire and plays an important role in passive fire protection. Intumescent coatings were first patented in 1948 and have been part of the building landscape since 1960.

An intumescent coating expands in a fire and forms a thick protective foam layer, called a char, that insulates the object from the fire. The foam forms a barrier between the fire and the object. Some intumescent products can expand to more than 100 times their original thickness. As the product expands, it becomes much less dense. It works as an insulator that keeps high temperatures away from structural components or protected openings.

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The chemical reactions that take place during expansion absorb heat. The coating reacts when its temperature reaches or exceeds 120 C (248 F), and the charring effect insulates and reduces the transmission of heat. It also releases water vapour to help cool the object.

The duration of protection of products with intumescent coatings differs but is generally between one and two hours. The load bearing capabilities of steel should not be impaired with that duration, allowing more time for evacuation and firefighter response.

Intumescent coatings contain several raw materials, including ammonium polyphosphate, melamine, pentaerythritol, and titanium dioxide. As the temperature rises, chemical reactions within the coating occur and forms the foam. As the char forms, the intumescent layer provides a barrier against the heat of the fire.

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One critical difference for specifiers is to distinguish between fire retardant and intumescent paint. Retardant paint slows flames from spreading and are meant for fires to self-extinguish. Intumescent paint creates the thick char barrier to insulate the structure behind the paint from fire and smoke.

Staggering statistics

Fires can start for a variety of reasons, but one of the most common is electrical fires. The National Fire Protection Association (NFPA) reports malfunctioning electrical work is the second leading cause of residential fires. Faulty or malfunctioning electrical systems caused 13 per cent of house fires from 2012 to 2016. Electrical arcing, when electricity jumps from one connection to another, is the most common heat source for fire. Electrical distribution systems, such things as outlets, switches, and cords, caused 48 per cent of all house fires.

In offices, electrical distribution and lighting equipment caused 12 per cent of fires from 2007 to 2011, according to the NFPA. Heating equipment caused 11 per cent.

The costs are also sky-high, with $1.3 billion of residential property damage caused per year by electrical fires, according to the Electrical Safety Foundation International (ESFI). Costs in commercial fires are even higher, reaching $2.4 billion per year. Data from 2017 indicates 95 deaths and 1,200 injuries occur each year from fires in commercial buildings.

In some applications, fire-rated doors allow access to electrical connections for repair, replacement, and maintenance. This is where understanding heat transfer and intumescent coatings is critical.

Fire-rated floor doors

Heat transfer and intumescent coatings are essential for specifiers to comprehend because fire codes pertaining to fire-rated floor doors are muddled.

Even the term “fire-rated floor door” can be confusing. While they are easy to overlook, fire-rated floor doors play an important role in passive fire protection, and there are distinct differences between various products on the commercial market. There are also different codes for doors used in a horizontal application.

Fire-rated floor doors are designed to contain the passage of smoke and flames per building code requirements. These products do not address exposure to excessive heat or hot gases and are only intended to confine fire for a set period. They are not tested or rated for heat transfer and are intended for installation in fire-rated floor assemblies only. They cannot be installed in fire-rated floor/ceiling assemblies per building fire protection code requirements.

Fire-rated access doors have a fire protective rating and are designed to prevent or retard the passage of excessive heat, hot gases, and flames over a period. Products are designed with intumescent coating on the underside of the cover and the inside of the frame to limit heat transfer.

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The coating seals the opening to ensure any combustibles stored on or near the door do not ignite due to excessive flame or heat transfer. Unlike fire-rated floor doors, these products can be installed in fire-rated floor/ceiling assemblies to maintain a building’s fire code compliance.

Understanding code requirements

In some cases, builders and architects have incorporated floor doors into the floor assembly for equipment access, removal, and installation in a horizontal plane. The view of building owners is that fire protection can be achieved in those applications if they place signage or barriers to prevent items being stored on top of the door, believing that fire safety risks are mitigated.

However, combustibles may be placed on the upper side of the door assembly, which could lead to a dangerous situation.

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Floor doors with a fire-resistant rating are generally available in larger sizes as they do not meet ASTM or UL heat transfer test requirements for a fire protection rating. While these larger access sizes may seem appealing to design professionals, the tradeoff is the reduced fire protection performance and the limited use in non-fire-rated floor/ceiling applications.

Conversely, fire-rated access doors, with the intumescent coating and ability to limit heat transfer, can be installed in both rated and non-rated floor/ceiling and roof/ceiling applications to maintain fire protection code compliance.

Due to heavy intumescent fireproof coating required to block heat transfer, these doors are commonly available in smaller sizes to ensure safe and easy operation. Products are available in sizes up to 1.06 x 1.06 m (3.5 x 3.5 ft), which generally meets most personnel and equipment access requirements inside of commercial buildings.

Code clarification

The difference between fire-resistant floor doors and fire-protective floor doors is addressed in several building codes.

International Building Code (IBC) 712.1.13.1 states horizontal fire door assemblies used to protect openings in fire-resistance-rated horizontal assemblies shall be tested in accordance with NFPA 288 and achieve a fire-resistance rating no less than the assembly being penetrated.

IBC 712.1.13.2 states access doors shall be permitted in ceilings of fire-resistance-rated floor/ceiling and roof/ceiling assemblies, provided that such doors are tested in accordance with ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials or UL 263, Fire Tests of Building Construction and Material, as horizontal assemblies and labelled by an approved agency for such purpose.

Commentary for this code states “Access doors are often necessary to service mechanical and plumbing systems above the ceiling. This section states that if such doors are used where the ceiling provides part of the protection, they must be tested in accordance with ASTM E119 or UL 263 as a horizontal assembly. This makes it clear that the standard fire test for doors (NFPA 80 or 257) is not acceptable. This ensures the thermal transmission through the access door and its effect on the assembly is considered. The provisions of this section are not applicable if the ceiling membrane does not provide any portion of the fire-resistive protection. Therefore, in a non-rated ceiling, this access door requirement would not apply.”

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It is important to note that floor doors with a fire-resistant rating cannot be installed in fire-rated floor/ceiling assemblies. Doors carrying the more stringent fire protective rating can be installed in both fire-rated floor and floor/ceiling applications to meet fire protection code requirements.

Several other codes are also important. For North American building codes, ANSI/UL 263 is the default standard for evaluating fire protection of structural steelwork.

ANSI/UL 263 and ASTM E119 were developed to simulate a building fire. The CAN/ULC-S101, Standard Methods of Fire Endurance Tests of Building Construction and Materials, provides equivalent test requirements for the testing of building materials to ensure market access across North America.

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These standards were developed to simulate the type of fires that occur in commercial buildings, such as offices, hospitals, and schools. These are often referred to as “cellulosic fires” due to the nature of the contents typically found in a commercial office building or multi-dwelling residence. At five minutes, the temperature within the furnace reaches 538 C (1,000 F). The temperature gradually increases during the duration of the test until at four hours, the temperature within the furnace reaches 1,093 C (2,000 F). This is the standard time/temperature curve for buildings.

ULC-S101/ASTM E119 is the standard test of building construction and material. These test methods are intended to evaluate the duration for which the types of building elements contain a fire, retain their structural integrity, or exhibit both properties during a predetermined test exposure.

A test specimen is subjected to a standard fire that is controlled to maintain a given temperature for a predetermined amount of time. When required, the fire exposure is followed by the application of a specified standard fire hose stream applied in accordance with Practice E2226, Standard Practice for Application of Hose Stream. The test provides a relative measure of the fire-test-response of comparable building elements under fire exposure. The exposure is not representative of all fire conditions because conditions vary with changes in the amount, nature, and distribution of fire loading, ventilation, compartment size and configuration, and heat sink characteristics of the compartment.

Variation from the test conditions or test specimen construction, such as size, materials, and method of assembly, also affect the fire-test-response. For these reasons, evaluation of the variation is required for application to construction in the field.

Staying safe

Code requirements are set at the lowest performance levels legally allowed for construction. Codes require which tests fire-rated doors must perform, as well as what performance level they must meet. However, if a product or assembly passes the minimum performance requirements and surpasses additional tests above and beyond what the code requires, it will offer the building owner and occupants more protection.

Fire protection officials and codes can do much to help ensure safety. It is, however, up to the building owners, construction teams, architects, and specifiers to invest in and properly install the appropriate fire safety products as intended for a particular application. Further, construction teams should confer with local officials to ensure compliance with Canada’s National Building Code (NBC) or local building codes.

Passive fire protection equipment plays an important part in keeping workers and owners safe. While differences in fire-rated floor doors are subtle in language, architects and specifiers need to be cognizant of how heat transfer and intumescent coatings are critical concepts to factor into building design.

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Steve Weyel is the director of sales and marketing for BILCO. The company has been serving the building industry since 1926 in the design and manufacturing of specialty access products.

Source URL: https://www.constructioncanada.net/evaluating-performance-of-fire-rated-floor-and-access-doors/

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