The Scandinavian countries have in later years seen several severe wildfires and is expected to exhibit more severe fire danger. While direct flame spread has been an important topic in wildfire research, there is a need for development and to ensure that experimental methods are relevant for Scandinavian wildfire characteristics. To ensure relevant lab conditions for fire-resilient material development work, large lab-scale (2×4 meters) experiments were conducted on various fuels. Its fire behaviour (such as rate of spread, fireline intensity and flame length) was compared with ongoing wildfire field studies from ongoing field studies in boreal and hemiboreal Sweden. The lab fire experiments show good potential to mimic relevant natural wildfire conditions in the laboratory once a standard design fire exposure for fire resilient materials is developed.

To reveal the flame intensification caused by foam agents extinguishing oil fires, inert gas foam generated by compressed nitrogen was used to extinguish oil pool fires, and the suppression mechanisms of the inert foaming gas on air mixing effect and flame intensification were investigated. The results show that nitrogen replaces the air in the foam, resulting in the inerting effect. At the same time, the released nitrogen dilutes the ambient oxygen concentration, producing the dilution effect. Due to the combined effects of inerting and dilution, the nitrogen foam reduced the extinguishment time by an average of 30.5 % and 32.1 % compared to compressed and aspirated air foams. For flame intensification, this work corrected the positive correlation between the dimensionless heat release rate increase and pool radius proposed by an existing study, and experimentally demonstrated that it is inversely proportional to 1/4 power of the pool radius. The dimensionless analysis shows that the flame intensification of nitrogen foam was reduced by approximately 30 % compared to air foam. Combining with experiments, it was found that the flame intensification of nitrogen foam was reduced by 25 %-36 % compared to air foam under the combined effects of inerting and dilution, of which the inerting and dilution effect accounted for approximately 20 % and 10 %, respectively. This study further corroborated the role of the air mixing effect in flame intensification and also found that the inerting effect remains generally stable with the change of experimental conditions because nitrogen replaces an equal volume of air. Therefore, the differences in the overall suppression effect of nitrogen foam on flame intensification mainly stem from the dilution effect.

Recent experiments have shown that exposed cross-laminated timber (CLT) can have a significant effect on the fire dynamics of large compartments. A simulation with the Fire Dynamic Simulator has been conducted to better understand the fire behaviour of open-plan compartments with exposed CLT. The simulation was set up to replicate a large-scale experiment, FRIC-02, with exposed CLT on the back wall and ceiling. The compartment was 95 m2 (18.8 m × 5.0 m × 2.5 m), with one long wall open (opening factor 0.18 m1/2). A continuous wood crib was used as the variable fuel load. The characteristic results of FRIC-02 with a rapid fire development and non-symmetrical external flames were successfully reproduced. With the wind coming diagonally from behind, as in FRIC-02, the external flames emerged mainly out of one window. The flames covered the entire window height, which effectively inhibited the inflow of air through that window. The imbalance in air supply also created large temperature differences throughout the compartment. With no implementation of wind, external flames and temperatures were more symmetrical. Despite a good match to FRIC-02, the method still has several limitations, including the adaption of the burning rate to the feedback from surroundings.

Fire safety in semi-automatic parking facilities

The main goal of this study is to contribute to increased safety in semi-automatic parking facilities. Semi-automatic parking facilities are parking facilities with a system for automatic stacking of cars, but in contrast to fully automatic parking facilities, these are not closed, compact, and unavailable for the public. The study is financed by The Norwegian Directorate for Civil Protection (DSB) and Norwegian Building Authority (DiBK). A fire simulation was conducted to compare fire spread in a semi-automatic parking facility to fire spread in an ordinary parking facility. The results indicate that the spread of fire from the car that was first ignited to another car happens approximately equally fast in the two scenarios. Thereafter, the fire spread faster in the semi-automatic parking facility compared to the ordinary parking facility. Although these results should only be considered as indicative, they do show that decreasing the distance between rows of cars can lead to a much faster fire spread. The simulation also shows that the size of a fire in a relatively closed-off parking facility is not necessarily controlled by the number of cars but by the access to air. Hence, the number of openings and properties of ventilation systems in such facilities are important factors to consider when assessing fire safety. A study of regulations and experiences with semi-automatic parking facilities in Norway and other countries as well as aspects that increase risks in semi-automatic parking facilities was conducted. No specific fire-related experiences were discovered, but this is not surprising when considering that fires in parking facilities are relatively rare and there are relatively few semiautomatic parking facilities. In addition, these types of facilities are relatively new. The study found regulations for fully automatic parking facilities in Norway, but semiautomatic parking facilities are not covered by the same regulations. The current regulations do not ensure that the authorities are informed when automatic car-stacking systems are installed in existing parking facilities that are open to the public. There are no regulations ensuring that a fire safety assessment is conducted when an automatic car-stacking system is installed in an existing building regulated for parking that is accessible to the public. It is our opinion that there is a need for a new assessment of fire safety when a system for car stacking is established in an existing parking facility.

Fire safety during construction and rehabilitation of buildings. This study deals with how the covering of buildings during the construction or rehabilitation of buildings affects fire safety and to what extent the regulations take this into account. The main focus has been mapping relevant requirements, recommendations, and performances related to the covering of buildings, mapping available materials, investigating the material’s fire properties, and modelling the spread of smoke within the covering. A mapping of the relevant laws and regulations applied for constructing and rehabilitating buildings has been carried out. The mapping has shown that demands are placed on owners, users, project owners, builders, businesses, employers, planners and contractors through many different laws and regulations. The people involved can have several roles, and similar roles have different names in the various regulations. For buildings in use, fire safety must be ensured for both the users and workers. It also applies that both the owner and the users are responsible for ensuring fire safety. It requires good communication and cooperation between different actors to ensure that fire safety is maintained for all involved, during the construction and rehabilitation of buildings. When covered scaffolding is used, the Regulations concerning the performance of work, use of work equipment and related technical requirements [10] require that the covering satisfy the fire requirements for materials used in escape routes (§17-20). The guideline to the Norwegian Regulations on technical requirements for construction works, TEK10, (Veiledningen til TEK10) §11-9, provides pre-accepted performance levels. For escape routes, class B-s1,d0 (In 1) is specified for walls and ceilings. There is no requirement for fire classification of the walkways in the scaffolding under the applicable laws and regulations. We believe there should be requirements for fire classification of the walkways, in the same way as for the covering, i.e., B-s1,d0 (In 1) for surfaces on walls and ceilings and Dfl-s1 (G) for surfaces on floors. The simulations of the spread of smoke from a fire inside a building during construction or rehabilitation show that the spread of smoke is affected when the scaffolding around the building is covered. Covering around the sides leads to a greater horizontal spread of smoke in the scaffolding than without covering. When the cover also has a roof, the smoke first accumulates underneath the cover's roof before it eventually also fills up with smoke down the floors of the scaffolding. The simulations showed that establishing an open field in the upper part of the cover would ventilate the smoke gases effectively, and the spread of smoke was essentially the same as for a cover without a roof. In addition, the simulation indicated that the air flow through the walkways in the scaffold could be an important factor in reducing the covering's negative effect on the spread of smoke. Of the 64 different products used for covering found in the survey, 35% had full classification according to EN 13501-1 (such as B,s1-d0). About 6% stated that the product was not flame retardant. Of the remainder, it was evenly distributed between those who stated a fire classification according to other test methods, those who did not provide any information on the fire properties and those who stated that the product was flame retardant without further specification. The mapping also indicates that the products from market leaders used by large general contractors provide products with documented fire properties. Conversations with two of Norway’s largest fire and rescue services shed light on several challenges connected to covering scaffolding and construction during firefighting activities. They pointed out that the covering could cause challenges and delays throughout their efforts. The covering gives a reduced visual overview of the spread of smoke and the location of doors and windows. This information is important for planning both extinguishing and smoke diver efforts. In addition, the covering can be an obstacle to the actual extinguishing effort, the use of an extinguishing agent and smoke divers and rescue efforts.

A series of model scale experiments were conducted to study the fire development in a ro-ro deck with various opening geometries. The experiments were performed in a 1/8 reduced scale model with a heptane pool fire as fire source. Experimental results show that both the ventilation factor and the opening position affect the fire development. The critical opening ratio for the fire to self-extinguish is 4%, with the opening locating at the bottom of the side walls while no self-extinction is found for other tests. A higher opening position and a larger opening height provide better flow exchange between the deck and the ambient, but this effect is only obvious for 4% opening. Numerical study shows that Fire Dynamic Simulator used with default simple settings underestimates the fire development and yields an early extinction when fire self-extinction occurs. For freely developed fire with large openings, FDS gives more close results to experiments.

This paper systematically studied the coupling effect of ambient pressure and tunnel slope on temperature distribution and smoke propagation in full-scale tunnel fires under natural ventilation by FDS. The downstream length (longitudinal length from fire source center to tunnel downstream exit) was also considered. The concept of “height difference of stack effect” was put forward when analyzing the mutual effect of tunnel slope and downstream length on smoke movement. The results show that the maximum smoke temperature beneath the ceiling decreases with the increasing ambient pressure or tunnel slope. The longitudinal smoke temperature decays faster with the decreasing ambient pressure or slope in inclined tunnel. The induced inlet airflow velocity increases with the increasing height difference of stack effect, while decreases with the increasing ambient pressure. And the smoke backlayering length decreases with the increasing height difference of stack effect. Taking heat release rate (HRR), ambient pressure, tunnel slope and downstream length into account, the prediction models of dimensionless induced inlet airflow velocity and smoke backlayering length in inclined tunnel fires at high altitude were developed, which agree well with our and others’ results. The outcomes of current study are great meaningful to fire detection and smoke control in inclined tunnel fires at high altitude. © 2023, The Author(s)

Blind roadways have only one portal which connects with other types of mine roadways. Sealing the fire area in a blind roadway is an effective method of disaster relief in a mine. To understand the effect of sealing ratio and sealing distance on fire behavior, Fire Dynamics Simulator (FDS 6.6) was used to study blind roadway fires with different fire scenarios. Results indicate that the smoke flow velocity increases significantly with the increase of sealing distance. The fire in the blind roadway is ventilation-controlled. When the sealing ratio reaches 80%, the fire self-extinguishes completely. Otherwise, the fire experiences an extinguishing-reburning cycle periodically. Besides, an empirical model is proposed to predict the downstream temperature distribution beneath the ceiling in the region from fire source to sealing position. The predictions by the proposed model comply well with the simulation and experimental results from our and others’ studies. This study provides new insights into the sealing strategies in blind roadway fires, and the outcomes of the current study are of guiding significance for the fire rescue in the blind roadways or similar structures. © 2022, The Author(s)

A series of 1:3 intermediate scale tunnel fire tests was performed to investigate the performance of a fully automatic sprinkler system in a road tunnel. The experiments were carried in a container tunnel with scaled geometry, using wood pallets as the fire source to simulate HGV fires. The activation of the sprinklers was simulated by using thermocouples that corresponded to a given Thermal Response Index (RTI) of a sprinkler bulb or a link. A total of 12 tests were carried out with varying longitudinal velocities (0.8–1.7 m/s), sprinkler activation temperatures (68–141 °C), water densities (2.9–8.7 mm/min) and types of arrangement of the fuel. The activation times, number of activated sprinklers, maximum heat release rates and other key parameters are presented and analyzed. The results show that the water density plays a key role in the performance of the automatic sprinkler systems tested. A high tunnel ventilation velocity, low water density and low sprinkler activation temperature are not recommended. © 2022 The Authors