Fire Safety

A fire in a building can develop very quickly and lead to devastating consequences. In the design process of a building and when selecting building materials it is therefore of greatest importance that the fire safety aspects are treated carefully and with knowledge.

  • Requirements on suspended ceilings
  • Fire safety in buildings
  • Description of a fire within a room
  • Testing and classification of products
  • The European system
  • The ASTM system
  • The suspended ceiling as fire protection in practice
Functional demands icon
  • The surface linings of walls and ceiling are crucial for the early develoment of a room fire
  • Flash over occurs at a temperature of about 600°C
  • The maximum air temperature for safe evacuation is appr. 80°C

 

Requirements on suspended ceilings

The fire safety demands on suspended ceilings can vary depending on both the type of room and building where they are to be installed. Detailed requirements can be found in the national building regulations. Three general requirements can, however, be identified as crucial for suspended ceilings in the early stages of fire. The first two should be regarded as "compulsory" in all premises, while the third is normally only required when the ceiling void contains relatively large amounts of combustible materials, e.g. cables.
  • They must only make a negligible contribution to the fire development and to the production of smoke. This is fulfilled by using a ceiling consisting of materials and surface linings complying with at least Euroclass B-s1, d0.
  • They must not break and collapse during the early stages of the fire when evacuation and rescue operations can still be carried out. To pass this requirement a ceiling system should be able to withstand a heat exposure of approx. 300°C. (The heat radiation from a smoke gas layer with a temperature of 300°C corresponds approximately to what a fully equipped fire fighter can withstand.)
  • They should prevent ignition of combustible material in the ceiling void in order to delay or prevent the occurrence of flash over. This requirement, as well as the second, is met with ceiling systems classified as class K1 10/K2 10 or as "Fire protection covering" according to NT Fire 003. 

Fire safety in buildings

The main purpose of the fire safety design of a building is to minimise the consequences of a fire. Principally, it concerns the prevention of injury to people but it also entails limiting the material and economic damage which is likely to ensue.
 
Functional demands, Fire safety, Initial stage of fire
In a burning building the circumstances can quickly become such that there is imminent risk of personal injury. Within the parameters of safe evacuation, consideration must be given to fire gases, visibility, heat radiation and temperature. E.g. in order to evacuate safely, the air temperature in rooms through which people are escaping should not exceed approx. 80°C.
 
The total fire protection of a building and its specific function is a complex issue, comprising several areas and how they interact with one another:
  • The building itself including its design, building elements, materials, interior fittings and furnishing
  • The fire detection systems and alarms
  • The organisation and practice of conducting evacuation, e.g. in schools and nursing homes
  • The rescue efforts of fire brigades
  • The extinguishing and control of the fire. Partly through automatic fire extinguishing systems and/or partly through active actions, e.g. of the fire brigade
Building regulations and various types of standards normally cover these aspects. The building regulations are formulated on a national basis and vary between different countries. Standards can be on either a national base (e.g. DIN, BS and ASTM) or international (EN- and ISO-standards). 

 

Description of a fire within a room

A room fire can be divided into various phases. The incipient phase or beginning of a fire is dependent on the size of the ignition source and the properties of the materials and objects that are directly affected.
During the growth phase the fire increases in size and other objects around the fire origin will begin to burn. Even the surface linings of the walls, floor and ceiling close to the fire can ignite. Increasing amounts of smoke and heat begin to develop and a layer of hot fire gases forms beneath the ceiling.
 
Functional demands, Fire safety, Growth phase of the fire
In the growth phase the fire is local. The fire characteristics of the surface linings play an important part in the fire development.
 
During the growth phase flashover can occur. This is when the intensity of the fire is so great that it ceases to remain local but involves all combustible material in the room. A large amount of heat is released and flames burst out through windows and door openings.
Generally, flashover occurs once the fire gases in the room reach 500-600°C. The heat radiation from the layer of fire gases is so great at this stage that it causes all combustible materials to ignite.
Flashover can occur just a few minutes after ignition. However, it can also be delayed or avoided altogether. This could be the case in a room which has just a small amount of combustible furnishings and is equipped with surface linings that make just a negligible contribution to the fire development.
After flashover the fire reaches its maximum level and is fully developed. The length and intensity of the fire is now mainly determined by the supply of air and the fire load, i.e. the amount of combustible materials present.
The decay phase is when the fire fades out.
 
Functional demands, Fire safety, Flash over stage of fire
At the point of flashover the entire room is engulfed by the fire and large flames burst out from door and window openings. The fire can now spread to other parts of the building.

 

Testing and classification of products

Fire testing methods are generally designed to simulate the different phases of the fire process. Consequently, tests on surface linings are conducted using fire sources representative of the incipient and growth phases of a fire. These test methods are referred to as "reaction to fire" tests and the purpose is to evalutate the contribution of products and materials to the early stages of a fire in terms of:
  • Ignitability
  • Flame spread
  • Heat release
  • Smoke production
  • Occurrence of flaming droplets/particles
Normally reaction to fire tests are carried out in small or intermediate scale.
Complete building elements (doors, floor structures, partitions etc.) which are used for separating fire compartments are tested for the case of a fully developed fire. These test methods are called "fire resistance" and are carried out in full scale. The temperature in the test furnace follows the so-called "standard fire curve" which is designed to represent a fully developed fire. The properties that are evaluated are:
  • Insulation (ability to reduce the heat transfer)  
  • Integrity (ability to prevent leakage of flames and hot gases)
  • Load bearing capacity
Building elements classified as "fire resistant" with respect to integrity and insulation are used as a means to prevent fire being spread between fire compartments.

 

The European system

Reaction to fire - Euroclass
The new reaction to fire testing and classification system for linings and materials in Europe is called Euroclass.
Altogether there are 39 classes divided into 7 main levels; A1, A2, B, C, D, E and F where A1 is the best and F are for products and materials not classified.
Most of the main classes also include an additional classification regarding smoke production and the occurrence of flaming droplets/particles.
The classes for smoke are s1, s2 and s3, where s1 is the best.
The classes for flaming droplets and particles are d0, d1 and d2, where d0 is the best.
 
Functional demands, Fire safety
1 = Main class
2= Smoke produktion
3 = Occurence of flaming droplets/particles
 
Euroclasses
Euroclasses according to classification standard EN 13501-1 Fire classification of construction products and building elements - Part 1 Classification using test data from reaction to fire tests.
 
 
Functional demands, Fire safety
1. Temperature
2. Flash over
7. Time
3. Incipient
4. Growth
5. Fully developed
6. Decay
8. Euroclasses and class K2 10
9. Fire resistance classes
The graph shows the relationship between fire process and the fire classes
 
Fire protection ability - class K
The information regarding class K reflects the situation of March 2003 when the working process with the European test and classification standard still was under progress. Changes may therefore have occurred.   
Class K comprises four classes: K1 10, K2 10, K2 30 and K2 60.
Class K1 10/K10 derives from and corresponds mainly to the Nordic testing and classification standard NT Fire 003 "Fire protection ability - Coverings". This class was developed and designed for evaluating the fire protection ability of coverings, such as suspended ceilings, in the growth phase of a fire.
The main reason for using a ceiling classified as K1 10/K2 10 is that it should prolong the time to flash over or even prevent it. This is achieved by not allowing any combustible material behind the covering, e.g. cables and timber members in a ceiling void, to come into contact with the fire and therefore contribute to its growth. This means that the fire development will only be governed by the conditions of the room itself.
The class also means that the ceiling, or parts of it, does not break and collapse during the time evacuation and rescue operations can be carried out.
If there is a need of extending the protection function over the flash over point into the phase of a fully developed fire class K2 30 and K2 60 could be used.
Contrary to the Euroclasses, class K includes the complete ceiling system i.e. panels, suspension hangers, fixings, perimeter trims etc. The Euroclass system is only concerned with the panels of a ceiling system, provided that the grid and other components do not contribute to the fire development, e.g. if they are made of metal.
 
Functional demands, Fire safety, illustration
1. From Norwegian/Danish "Kledning / beklaedning" (covering)
2. Number of minutes of fire test.
10 minutes represents the early stage of fire. The fire gas temperature in the test furnace reaches appr. 680° C which is over the critical temperature for flash over.
 
Fire resistance
The main classes used for the fire resistance classification of building elements are:
R = Load bearing capacity
E = Integrity (ability to prevent leakage of flames and hot gases)
I = Insulation (ability to reduce the heat transfer)
The classes are always combined with a time class expressed in minutes. These time classes could be from 15 up to 360 minutes in steps defined in the classification standard EN 13501-2. A separating and load bearing wall could for example be classified as REI 60, which means that it will retain its load bearing capacity as well as its fire separating function during 60 minutes of a fully developed fire.
A non-load bearing element will only be given the classification EI or E combined with a time class. The latter case is for example relevant for special fire glazed partitions which will prevent the penetration of flames and hot gases but not provide insulation against heat. A load bearing column, which is obviously not a separating element, can, accordingly,  only have the fire resistance class R combined with a time class.
 
Functional demands, Fire safety
1 = Load bearing capacity
2 = Integrity (ability to prevent leakage of flames and hot gases)
3 = Insulation (ability to reduce the heat transfer)
4 = Time class in minutes

 

The ASTM system

Reaction to fire
In the US market products are tested and classified according to ASTM standards (American Society for Testing and Materials).
Flame spread and smoke production of surface linings, for example on ceilings, are tested and evaluated according to ASTM E 84 "Surface Burning Characteristics of Building Materials". A smoke production index and flame spread index is then derived from the measurements that are taken.
(The test apparatus consists of a 25 feet (7.6 m) long horizontal "tunnel furnace" with a cross sectional area of approximately 12'1/2 x 17'3/4 in (305 x 450 mm).The interior surfaces are covered with the test material and a burner is applied at one end of the tunnel. In the other end there is a fan creating a draft forcing the flames to propagate into the tunnel. The test lasts ten minutes.) 
Acoustic ceiling products are classified according to ASTM E 1264. Three fire classes are defined; A, B and C. The classes are equivalent to classes I, II and III, respectively, of various building code authorities. Class A (I) is the best.
 
ASTM fire classes. In addition, for class A ceiling products the material should not show evidence of continuos progressive combustion after the test flame has been extinguished.
 
Fire resistance
Fire separating elements, such as fire walls and floor structures, are tested and evaluated in accordance with ASTM E 119  "Fire Tests of Building Construction and Materials". The tests are carried out in full scale. The test specimens are subjected to a heat exposure that corresponds to a fully developed fire.

 

The suspended ceiling as fire protection in practice

Class K1 10/K2 10 (Fire protection covering) and Euroclass classifications play a crucial role in the early development of fire and consequently for the fire safety of a building as a whole. In order to obtain the required functions the assembly instructions and other conditions included in the classification must be followed at the building site.
Class K1 10/K2 10 is a classification, which, unlike the surface lining classifications, encompasses the complete structure, i.e. panels, grid, suspension hangers, fixings and other included components. None of the components incorporated in the ceiling system may be changed in any way without risking the validation of the classification.
Even if the surface lining classifications are not as tightly bound as class K1 10/K2 10 to the constructional design of the ceiling, there are still limitations. For example, any kind of repainting or alteration of the surface will make the classification of the surface lining invalid. Furthermore, repainting will also have an effect on other properties, such as sound absorption.


Ceiling integration

Many technical services are located in the ceiling area and must satisfy both aesthetics and function. Co-ordination of details must take place early in the design stage.