Energy efficiency and the overall need for sustainable buildings are increasing the use of efficient thermal insulation systems. In national regulations and guidelines limitations or protection requirements may be specified for the use of combustible insulation in façades. Alternatively, there may be performance-based requirements for products or for the whole façade system defining fire performance levels for different applications.
The effect of the EPS ETICS system on fire safety has been studied by using fire safety engineering methods for residential multi-storey buildings up to eight floors. The probabilities of the spread of the fire to apartments above the room of fire origin were assessed by calculating heat exposures and consequences caused by the external flaming both for the EPS ETICS façade and for façade made of at least A2-s1, d0 materials.
In this study it is assumed that EPS insulation is protected from internal fires by structures with fire-separating function of at least EI 30. EPS insulation is protected from external side by an approved reinforced rendering system (ETICS, which fulfil requirements of ETAG 004 including fire performance of components and the system). Fire stops are used to prevent a fire spread in the insulation layer in buildings with more than two floors.
Statistics
To establish the statistical basis for studying the effect of EPS insulation used in external wall on the fire safety of the building, a statistical survey was carried out on the data stored in the statistics system of the Finnish rescue services (PRONTO) and in the statistics database of the Swedish Civil Contingencies Agency (IDA). The survey concerned fires in residential multi-storey buildings and the years covered in the survey are 2004 – 2012 for PRONTO and 2004 – 2011 for IDA.
According to statistics, the fire is extinct without fire brigade intervention (and thus not capable of spreading out of the compartment of fire origin) in about 15 – 30% of the fires. By the arrival of the fire brigade, the fire development situation is the following: the fire spread outside the fire compartment: from 1% (Sweden) to 3 – 4% (Finland) per ignited fire. Information on fire spread due to window breaking (according to Finnish statistics) indicated that 0.7% of cases could lead to spreading through windows.
Fire performance of EPS under different fire conditions
Fire performance parameters for white and grey (containing carbon/graphite) EPS with and without flame retardants were measured using the cone calorimeter method and compared with literature values. At the heat flux level of 50kW/m2 there are only small differences between the products with and without flame retardant. The efficiency of flame retardant is especially significant at lower heat fluxes: flame retardant EPS did not ignite at 20kW/m2 but without flame retardant it ignited at 15kW/m2. The experimental results also show very clearly the protective effect of a thin (about 5mm) non-combustible layer.
The EPS insulation is protected with reinforced rendering (5 - 8mm), which does not ignite or the contribution to fire of which is limited. Based on experimental results, 50kW/m2 is used as an average value for rate of heat release from rendering-protected EPS in the simulations. In the sensitivity analysis a double of the value, 100kW/m2, is used to cover possible worst case scenarios.
There is also large scale experimental evidence on fire performance of EPS-rendering systems made in the following scale/conditions: specimen size above fire room 5 – 6 m and fire load 300 – 600MJ/m2. Maximum heat flux at the window above fire room, maximum temperature at the upper edge level of the specimen and limitation of burnt area to the lower edge of the window two floors up from the fire room are examples of acceptance criteria in these tests. In successful experiments EPS has contributed to the fire only on a limited area and no fire spread beyond the two floors above the fire room has occurred.
Simulation results of fire spread
The comparison of probabilities for at least A2-s1, d0 and EPS insulated façades are shown in Figure 1 as cumulative probabilities. The second floor window was broken in 31 ± 5% with at least A2-s1, d0 façade and in 36 ±5% of the cases with EPS insulation. Until about 25 minutes from the start of the fire the window breaking time probabilities for both façade types are very close to each other (within one minute difference). For the third floor the final probabilities were the same (5 ±1 %), but with EPS insulation the window breaking tends to occur slightly earlier. These are relative numbers per fires which have spread through the fire room window to the façade.
The accident statistics based limit value for probability of fire spreading to the apartments above is compared with event tree analysis estimates in the bottom part of Table 1. The sum for probabilities of breakage of window 1 and 2 floors above were calculated to be 1.9% for at least A2-s1, d0 façade and 2.3% for EPS ETICS façade per ignited fire. So for a A2-s1,d0 façade, one out of 52 fires spreads to the next storey and for an EPS ETICS façade this is one out of 44 fires spreads to the next floor. These estimates are on the upper limit of statistical data for which conservative values were used. Thus a safety factor is included in the results.
| Probablities in the branches of event tree and overall probabilities | Statistical data (At least/nearly A2-s1, d0 façade) |
Data used and results of simulations (At least A2-s1, d0 façade) |
Data used and results of simulations (Rendering + EPS insulation) |
| Early detection of fire | 0.70 | 0.7 | |
| First-aid extinguishing successful | 0.15 - 0.25 | 0.20 | 0.2 |
| Self-extinction of fire | 0.10 - 0.15 | 0.15 | 0.15 |
| Fire brigade extinguishes fire before spread via window | 0.80 - 0.95 | 0.90 | 0.90 |
| Fire spreads via window | 0.73 | 0.73 | |
| Breakage of window one floor above of fires spreading via window | 0.31 | 0.36 | |
| Breakage of window two floors above of fires breaking window one floor above | 0.16 | 0.16 | |
| Overall probabilities | |||
| Breakage of window one floor above | 1.66% | 1.95% | |
| Breakage of window two floors above | 0.26% | 0.31% | |
| Breakage of window one or two floors above | 0.7% - 2% | 1.9% | 2.3% |
Performance criteria for life safety
A common way of expressing risk is an F-N curve, where the frequency (F) of an incident is plotted as function of the number of fatalities (N) for that incident. An example of F-N curve of fire fatalities illustrating the significant differences in acceptance levels between single and multiple casualties is shown in Figure 2.
Concerning consequences for life safety the fire death probability was found to be not more than 10-6 per building fire (0.8∙10-6 for at least A2-s1, d0 façade and 1.0∙10-6 for EPS ETICS systems). When this value is compared with tolerable limit of F-N-curves,2 it can be concluded that life safety objectives are reached.
Safety during construction/renovation
Uncovered EPS with flame retardant can resist small ignition sources such as cigarettes or small flames and is classified for reaction to fire as Euroclass E. Also under radiant exposure at low heat flux levels EPS with flame retardant is superior to EPS without flame retardant in terms of fire behaviour. At higher heat fluxes these differences are reduced and at 50kW/m2 the differences are not significant.
The main principles and actions concerning construction site fire safety for the time when EPS is uncovered during installation phase can be summarised as follows: a) Reduce the risks of ignition by good building site management and by minimising the fire load, b) follow the hot work instructions, c) make sure that everybody involved understands all fire safety instructions and d) if the apartments are occupied during the installation process, limit the time EPS insulation is uncovered and provide proper safety instructions and means for escape.
References
1. Mikkola, E., Hakkarainen, T.; Matala, A. 'Fire safety of EPS ETICS in residential multi-storey buildings.' Espoo: VTT Technical Research Centre of Finland, 2013. 37 p. + app. 4 p. (Research Report VTT-R-04632-13.)
2. Korhonen, T; Hostikka, S; Keski-Rahkonen, O. 'A proposal for the goals and new techniques of modeling pedestrian evacuation in fires,' Presentation at 8th International Symposium on Fire Safety Science. Beijing, China, 18 - 23 Sept. 2005. Gottuk, D. & Lattimer, B. (eds.). International Association of Fire Safety Science (2005), 557 - 569.
