The exposure component in FRAME.   The EN954-1 approach of risk evaluation indicates that a higher level of protection reliability is required when the exposure of the subjects to the risk is frequent or prolonged. There is thus a requirement for some measurement of the exposure.  As fire is a rather rare event, the main consideration that defines life safety in fire situations will be the exposure time. For the activities, the duration of the fire is only one element: the consequences of a fire are not ended when the fire is out, the business interruption or reduction can continue for several months, the reconstruction time for a building can be very long, and unique objects can be destroyed for ever. These considerations have resulted in three slightly different formulas in FRAME to calculate the exposure, one for the property, one for the people, and one for the activities.  Exposure for people   Usually people are considered to be safe, when they have left building on fire: the most evident measurement for the exposure is the evacuation time. But experience learns that the fire propagation in a building is not a uniform phenomenon and that rapid fire spread is the major reason for fire victims. This means that to evaluate correctly the exposure of people, evacuation time and fire propagation shall be jointly considered. In FRAME this results in the formula: A1 = {1.6 – a} - ( t + r )   The most significant factor for fire spread is the presence of ignitable surfaces, mostly building finishing and packaging materials. This is the reason why FRAME uses an r-factor, calculated with the immobile fire load Qi (building materials) and the combustibility factor M (for the surface conditions). The evacuation time shall be calculated for the actual conditions of the compartment and its occupants. The t-factor in FRAME does this, considering the whole path from the most remote corner of the compartment to the outside of the building, the capacity of the occupants to move, and the compression effect when too much people use the same path. The formula is derived from scientific evidence on evacuation speed (ref. Engineering Handbook, indicates speed S = k - a.k.D). The p-sub factor increases the total evacuation time for unfavourable conditions, such as lack of awareness, reduced mobility and confusion. One of the main issues in the assessment of the fire safety of a building is to check if the building can be evacuated safely in case of fire. One way to do this is to compare fire scenarios with evacuation scenarios. The fire scenario will define a Available Safe Egress Time or ASET, and the evacation scenario will define the Required Safe Egress Time or RSET. The fire safety level is considered to be acceptable when there is a sufficient margin between both time calculations. FRAME has a slighly different approach. It uses a formula that calculates a conservative required egress time and compares this with a target time, which depends on the fire conditions. The value of the acceptable risk is then adjusted according to this comparison, the higher the difference, the more evacuation protection will be required to balance it. For more on evacuation time assessment, look here ... One additional consideration that has be been built in FRAME is the fact that multiple death accidents are considered to be far more unacceptable than single death situations. Some researchers in social behaviour claim that the risk acceptance is reduced by the square value of the number of possible deaths. Multiple deaths in a fire are likely to occur where long evacuation times come together with rapid fire spread. The combined values of high t- and r-factors will result in a value of A <1, which means an increase in fire risk. In such situations, protective action must be taken to counteract the exposure; the effect of such action is reflected by the value of U, the escape factor. Exposure for property  To measure the exposure for property, FRAME uses basically the monetary value of the property, transformed in the c2-factor. A similar approach exists in the insurance industry where an additionally premium is asked for high value properties. This practice is unusual for property values below 7 to 8 million Euro / US Dollar, which is also the lower limit used by FRAME. A correction is added to reflect the uniqueness of the content by the c1-factor. An additional consideration made in FRAME is the fact that fire brigades will give priority to saving the occupants before starting large fire extinguishing operations. This means that lengthy evacuation will in fact increase the exposure for the property. The result is the formula: A = {1.6 – a} - (t + c1 + c2) Exposure for the activities. An often-neglected aspect of fire risk is the business interruption potential. In fact, code requirements do not consider at all the impact of a fire on the economic life of a building. In the past, mostly insurance companies and corporate risk managers were concerned about it. Fire was easily accepted as a fortuitous event (an act of god), business interruption insurance was optional, unemployment after a fire was not a social issue. Risk managers have spent a great deal of their efforts to bring business continuity after fire in the picture, and more recently authorities have become more concerned about the impact of fire on vital constructions such as major hospitals, power plants, ministries, road tunnels etc.  FRAME deals with this aspect of exposure in the following way. The duration of a fire is less important for its impact on the activities, as even a partial fire can stop an activity for several months, particularly if toxic combustion products like dioxins would be generated. Because of this "partial fire" consideration, the fire load factor q was not retained in the potential risk P2, as well as the correspondingly most effective protection (fire resistance) F for the protection degree D2.  The most evident elements for assessing the impact on a fire are also the monetary loss and the uniqueness of the content, so the c- factor is maintained. The evacuation time is not important for this issue. In reality, it appears that large losses in storage buildings do not have a big impact on business interruption, but that fires in controlling areas and bottleneck installations are very critical. A measure for this was found in the "added value/ turnover" ratio, used as d-factor. It gives a good indication of the dependency of an activity on a certain location. The result of these considerations is the formula: A2 = {1.6 – a} - (c1 + c2 + d)   An increased exposure for the activities can be compensated by a general improved fire protection, but also by specific local protection systems for bottleneck operations and by organisational measures to reduce dependency from one location, to relocate the business or to speed up restarts. These considerations are the basis for the specific formula for D2 = N.W.S.Y. PRINT  THIS SECTION  (pdf)