Understanding Integrity, Stability and Insulation in Passive Fire Protection
Fire resistance is not a property of an individual material, but the measure of the performance of a complete system or construction when exposed to standard heating conditions. When evaluating and selecting a passive fire protection system, there are three essential performance criteria that are tested for against BS 476: Parts 20 to 24 (or equivalent), and which should be carefully considered in order to make a compliant selection – stability, integrity and insulation.
Stability refers to an element or system’s capacity to resist collapse due to loss of structural strength caused by exposure to fire, or more specifically, the heat generated by a fire. The element should remain structurally stable for the denoted duration.
Failure is deemed to have occurred if the element collapses in such a manner that it no longer fulfils its intended function, or loses its load-bearing capacity during the denoted duration. For example, “R120” denotes that the system will not collapse and will remain stable for 120 minutes when exposed to a fully developed fire.
For an element to achieve an integrity rating, stability is assumed as a mandatory base factor – if a system loses its stability and collapses, it automatically loses its integrity performance ability. Therefore, the stability rating is often not explicitly denoted, as it is assumed to be at least equal to the integrity rating. For example, “E120” explicitly denotes that the system will achieve 120 minutes’ integrity, and therefore also achieves 120 minutes’ stability.
Integrity refers to an element or system’s ability to stop the flames or hot gases of a fire from physically passing from one side of the element (the fire side) to the other side (the non-fire side) through holes, gaps, cracks or any other types of openings. The element should stop flames and hot gases from passing through the element for the denoted duration.
Failure is deemed to have occurred if flames or hot gases physically pass from one side of the element to the other side during the denoted duration. For example, “E120” denotes that the system will not allow flames and hot gases from physically passing through the element for 120 minutes.
Insulation refers to an element or system’s ability to limit the surface temperature rise on the non-fire side of the element to 140°C as an average, or 180°C as a hot-spot maximum, for the denoted duration during which the fire side is exposed to a fully developed fire. The temperature readings are taken using Thermocouples attached to various locations on the element’s surface.
Failure is deemed to have occurred if either the average or the maximum temperature is exceeded during the denoted duration. For example, “I120” denotes that the surface temperature on the non-fire side of the element will not exceed 140°C as an average, or 180°C as a hot-spot maximum, for 120 minutes when the fire side is exposed to a fully developed fire.
The above short references of “R”, “E” and “I” – followed by a number to represent the duration in minutes – are commonly used within the fire protection industry when referring to BS 476 criteria.
These can be shortened further by combining the “E” and “I” where both ratings are equal – for example, “EI120” is used to denote that the system is both integrity and insulation rated for 120 minutes (and hence automatically deemed stability rated for an equal duration), rather than writing “R120 E120 I120”.