‘Fire-rated doors’ – what does it mean?

This article describes the fire-rated door and the fire-resistance testing and classification process, and provides an explanation of the EN standards approach. It answers why it is essential for fire-rated doors to be tested from both sides (bi-directional testing) and why classification is a separate part of the whole process.

Doors are used everywhere around us. Different buildings and different purposes mean that certain building elements may have additional requirements. The primary function of each door is to give access to the inside of a compartment. The type of building and the type of compartment defines the properties of the door that must be installed. 

Doorsets with fire-resistance characteristics (fire rating) are installed in openings within vertical separating elements (fire barriers). These doors provide the most important function by protecting life, preventing fire and smoke from spreading between compartments. 

Fire doors are a complicated product consisting of many engineered elements. Therefore, we cannot assess fire-rated doors based on a simple combustibility test. Instead, destructive tests are needed to prove fire performance. Fire door performance characteristics can only be assessed during testing in an accredited fire-testing laboratory, which provides testing according to standard methods. The standard test method is BS-EN 1634-1, which, in conjunction with product standard BS-EN 16034, provides a guideline for manufacturers to offer products with fire resistance performance characteristics for a certain period (fire rating). 

National Regulations govern requirements for resistance to fire of doors and the minimal fire rating; in the UAE, these rules are stated in the UAE Fire and Life Safety Code of Practice. 

Types of doorsets

Regardless of the number of manufacturers, we can group doorsets by type within the context of testing. Different doorsets require different approaches when selecting the most representative sample for testing. We can recognize several types of door, such as: 

• Wooden door leaf with wooden door frame
• Wooden door leaf with steel door frame
• Steel door
• Glazed door (metal framing)

Regardless of what type of door we are installing, we need to remember that fire-rated doors perform their most important function – resistance to fire – only while closed. Therefore, they must be equipped with devices that enable self-closing in case of fire. 

The construction of a doorset defines its rating, and the assembly process raises possible challenges during fire tests. Each product must be carefully designed as every component is related. One of the widely used fire-rated doors is a metal-framed glazed doorset. This product type is mainly made of profiles, where one or more chambers are filled with insulation material. Incorrect installation or fixing methods can be a reason for failure during fire tests. 

Testing of fire-rated doors

All types of doors intended to be used as pedestrian fire-rated doors must be tested in an accredited fire-testing laboratory (e.g. Emirates Safety Laboratory). Before the sample is installed in the supporting construction (simulation of the wall/fire barrier) – a discussion about the end-use application should take place between the manufacturer, laboratory and certification body and cover all essential aspects, e.g. door construction, installation and scope of application. The outcome of this review for the end-use application is crucial and affects the test numbers and the structure of the tested specimen, so it must be done before the test. Fire-resistance tests are conducted on representative samples, which are selected based on analyses of the direct field of application (specified by BS-EN 1634-1) or extended field of application based on the relevant part of Extended application standards (BS-EN 15269) for the analysed type of doorset. 

For pedestrian doorsets, the generic performance characteristics (unrelated to the fire-resisting characteristic) are defined by BS-EN 14351-1 or BS-EN 14351-2.

Requirements for pedestrian doorsets with fire-resisting characteristics are stated in the following standard: BS-EN 16034 Pedestrian doorsets, industrial, commercial, garage doors and openable windows – Product standard, performance characteristics. Fire resisting and/or smoke control characteristics.

Classification of fire-rated doors is specified in the following classification standard: BS-EN 13501-2 Fire classification of construction products and building elements – Part 2: Classification using data from fire resistance tests, excluding ventilation services.

In buildings, we can find fire doors that are manually or power operated and:

• used in a normal mode of operation,
• customarily held open and self-closed in the event of a fire, or
• closed in a normal mode of operation.

The second group of fire-rated doors must be subjected to the ‘Ability to release’ performance test before the fire-resistance test (according to BS-EN 16034). The test result is expressed as ‘released’. 

Notwithstanding the operation type, for each doorset before the fire test, mechanical pre-test conditioning should be undertaken (BS-EN 1634-1). 

Every product submitted for testing is subjected to standardised fire conditions provided by specialised furnaces. The heating of the specimens follows the equation for the standard time-temperature curve, defined by, for example, BS-EN 1363-1 or ISO 834-1:

T=345∙8t+1+20 [°C]

This represents a fire scenario in the flashover compartment (‘cellulosic fire’) where after 90 minutes, the temperature is above 1,000°C (1,832°F).

During the fire test, the doorset is assessed by the following criteria:

• Integrity (E): 

This is the ability to withstand the fire from one side and prevent the passage of flames to the unexposed side and prevent the development of gaps through which transmission of hot gases can be observed (BS-EN 1363-1). Integrity is expressed with the letter ‘E’. 

• Insulation (I):

This is the ability of a test specimen, when exposed to fire on one side, to restrict the temperature rise of the unexposed face to below-specified levels (BS-EN 1363-1). There are two applicable limits: average temperature rise (limitation: ≤140°C) and maximum temperature rise. The limit for the maximum temperature rise is different for the door leaf (≤180°C) and for the door frame (≤360°C). 

If a doorset incorporates areas of different thermal insulation (bigger than 0.1m²), these discrete areas must be assessed separately. Insulation is expressed with the letter ‘I’ and subscript number 1 or 2 (e.g. I₂). The code ‘I₂’ means the thermocouples are placed not closer than 100mm from the edge of the door leaf, whereas ‘I₁’ is the additional requirement which changes the limit for the door frame to ‘≤180°C’ – only when requested by the Test Sponsor or specific building regulations. 

An example of the arrangement for the temperature measuring points is shown in Figure 1. Points 1–5 are used to assess the average temperature rise, points 6–10 and 16–20 are used to evaluate the maximum temperature rise. Thermocouples Nos. 11–15 are placed 25mm from the door-leaf edge, assessing insulation for the ‘I₁’ classification. 

• Radiation (W):

This is the ability to withstand fire exposure on one side only and to reduce the transmission of fire as a result of significant radiated heat to adjacent materials (BS-EN 13501-2), with a limitation of 15kW/m². 

Radiation is expressed with the additional letter ‘W’, e.g. EW. 

The fire-resistance test of doors requires two specimens tested from both sides (one from each direction) unless the doorset is fully symmetrical except the edges (e.g. lock/leading edge and hinge edge or double rebated doors). Fully symmetrical means: the construction of the doorset is identical on both sides of the centre line of the cross-section. For such doors, BS-EN 1634-1 provides rules for some door types to minimise the number of tests based on the following premises:

• each of the door leaves is of symmetrical construction except for the edges,
• any restraining/supporting elements of building hardware have been included in a test under BS-EN 1634-1 when exposed in both directions so that they will retain their function when exposed to furnace conditions,
• there is no change in the number of leaves or the mode of operation (e.g. sliding, swinging, single action, or double action). 

The main reason for such rules is that the behaviour of the doorset is strictly related to the type of door leaf and door frame. For example, we can take two generic groups of hinged doorset: timber leaves in timber frames and metal leaves in metal frames. Each reacts differently during fire conditions; consequently, the weaker side (direction of the exposure to fire) is not necessarily the same for all of them. Furthermore, during such an assessment, we need to consider the ‘weaker side’ separately in terms of integrity and insulation performance. Therefore, each type of doorset must be assessed individually. The influence of the wall (fire barrier) they are installed into cannot be omitted. An example of the influence of the supporting construction is shown in Figure 2 – timber leaf, metal frame and opening into the furnace installed in the flexible wall (drywall). Due to the nature of the burning process, the timber construction of the door leaf is shrinking and tends to deflect towards the fire at its horizontal edges (at the top and bottom of the door leaf) – bending the door leaf towards the fire. Timber door frames will react similarly; however, fixing to the wall and different cross-sections make it stiffer, and therefore the door frame may not deflect with the same speed and in the same way as the door leaf. Having the door open towards the fire, the risk of passage flames on the unexposed side (out of the furnace) increases due to the overpressure at the top of the door, which will cause integrity failure. Doors opening outward from the fire will behave in the same way – the top and bottom edges will deflect to the fire, as well as towards the door stop, which will positively impact the test results. 

For assessing the weaker side, the type of supporting construction will not make a significant difference for the timber door frame. A rigid low- or high-density wall will restrain the frame against deflection, and a drywall partition will attempt to deform the door frame in line with the wall deflection. However, a bigger cross-section of most door frames will resist the forces of flexible supporting construction – consequently there is no significant difference between fire barrier types. 

The case of a doorset with timber door leaf and metal frame differs regarding the interaction between these parts. Due to the elongation of the metal frame caused by the heat, the bending of the frame will be toward the fire. The timber door leaf will bend in the opposite direction to the frame. If the door leaf is opened towards the fire, the horizontal edges will deflect to the fire side, moving away from the frame. The contrary movement of the metal door frame will exacerbate this. A rigid supporting construction (e.g. AAC or concrete masonry wall) will tend to restrain the movement of the wall (subject to adequate fixing). In contrast, the partition wall will enhance the level of deflection of the frame as it will deflect in a similar way. Thus, the weakest arrangement is a metal frame with a timber door leaf opening towards the fire and installed in flexible supporting construction. 

From an integrity perspective, for both doorsets the weaker side is recognised as the door leaf opened towards the fire. However, with regard to insulation, the outcome is not so obvious. As timber is inherently an excellent thermal insulator, a timber doorset shows no significant difference depending on which side is exposed. Thus, for doorsets with metal doors, there is no clear weaker exposed direction. Insulation performance can be assessed only during a bi-directional test. 

A metal doorset (metal door leaf in a metal frame), as it is made of the same material, will tend to similar behaviour – bending towards the fire with all door-leaf corners deflecting away. In terms of integrity installation in a rigid wall, due to restraining the frame – only with the proper fixing method, where the door leaf is bending to fire (corners moving away from the door stop), where flexible wall follows the deflection of the door assembly, it might be assumed that the more severe side is the door leaf opened outwards from the fire and fixed in a rigid wall. However, many factors shall be considered, and there can be exceptions to these conditions. 

The assessment of the weaker side in terms of insulation is different for each part of an assembly. Installation of a door leaf opened towards the fire might be worse for the door leaf. However, if the door leaf opened outwards, the fire might be worse for the door frame as more surface is exposed to heat. Therefore, a bi-directional test must be done to evaluate the insulation criterion. 

Classification of fire-rated doors

After the successful fire-resistance test, the laboratory issues the test report with a detailed description of the door construction and installation method. This document presents only the test results, which means it does not include classes of the product and is instead used as a basis for the classification process. 

The classification report deals with the ‘Field of direct application of test results’; where applicable, it includes an extended field. The extended field of application is based on the additional document: Extended application report of results from fire-resistance tests.

The direct or extended field of application of test results is a standardised set of rules defining the allowable changes of the product. These changes, for example, deal with the following: 

Table 1. Overrun time requirements.
Classification time (min)	Overrun time(all criteria must be fulfilled)
15	18
20	24
30	36
45	52
60	68
90	100
120	132
180	196
240	260

• application of the test results for the door assembly tested in one of the standard supporting constructions to a different type of supporting construction may or may not be applicable, 
• permissible size variations, where the allowable changes depend on the test duration time (only classification time or extended – overrun time – was reached with all criteria fulfilled). 

The classification standard BS-EN 13501-2 defines classes and classification periods (fire rating).

The code used to express the classification is presenting as below: 

E

I

W

t

t

Table 2. Fire resistance classes for ‘fire-rated’ doors.
Classes	Classification time in minutes (time of rating)
E	15	20	30	45	60	90	120	180	240
EI1	15	20	30	45	60	90	120	180	240
EI2	15	20	30	45	60	90	120	180	240
EW		20	30		60	90	120

tt – classification period for which all relevant criteria are fulfilled. 

Classification for fire doorsets is a combination of designatory letters and performance times only, as per Table 2, related to doors (e.g. EI₂ 60, EW 90). The classification report is the basis for the certification process. It is the document that allows the certification body to issue the certificate with the correct identification of fire-resistance classes of the doorset subjected to certification.

References

1. BS-EN 1363-1 Fire resistance tests – Part 1: General requirements
2. BS-EN 1634-1 Fire resistance and smoke control tests for door and shutter assemblies, openable windows and elements of building hardware – Part 1: Fire resistance test for door and shutter assemblies and openable windows
3. BS-EN 16034 Pedestrian doorsets, industrial, commercial, garage doors and openable windows – Product standard, performance characteristics. Fire resisting and/or smoke control characteristics.
4. BS-EN 13501-2 Fire classification of construction products and building elements – Part 2: Classification using data from fire resistance tests, excluding ventilation services.
5. BS-EN 14351-1 Windows and doors – Product standard, performance characteristics – Part 1: Windows and external pedestrian doorsets
6. BS-EN 14351-2 Windows and doors – Product standard, performance characteristics – Part 2: Internal pedestrian doorsets
7. P. Sulik, D. Izydorczuk (2015): Fire resistance of steel doors. ‘Materialy Budwlane’: No. 5/2015.