Entry resistance in smoke detectors was investigated using experimental and analytical approaches. The experimental work consisted of measuring velocity inside the sensing chamber of smoke detectors with a two-component Laser Doppler Velocimeter and exposing addressable smoke detectors to four different aerosol sources. The velocity measurements and exposure tests were performed in NIST's Fire Emulator / Detector Evaluator under steady state flow conditions in the range of 0.08 to 0.52 m/s. The addressable detectors were a photoelectric and an ionization detector. A specially constructed rectangular detector model was also used for the interior velocity measurements in order to have geometry compatible with numerical approaches, such as computational fluid dynamics modeling or a two-dimensional analytical solution. The experimental data was used to investigate the fluid mechanics and mass transport processes in the entry resistance problem. An inlet velocity boundary condition was developed for the smoke detectors evaluated in this study by relating the external velocity and detector geometry to the internal velocity by way of a resistance factor. Data from the exposure tests was then used to characterize the nature of aerosol entry lag and sensor response. The time to alarm for specific alarm points was determined in addition to performing an exponential curve fit to obtain a characteristic response time. A mass transport model for smoke detector response was developed and solved numerically. The mass transport model was used to simulate the response time data collected in the experimental portion of this study and was found, in general, to underestimate the measured response time by up to 20 seconds. However, in the context of wastebasket fire scenario the amount of underprediction in the model is 5 seconds or less which is within the typically polling interval time of 5 to 10 seconds for an addressable system. Therefore, the mass transport model results developed using this proposed engineering framework show promise and are within the expected uncertainty of practical fire protection engineering design situations.

This report describes an investigation into the prediction of the activation times of domestic ionisation and photoelectric smoke detectors within a two storey dwelling, the work undertaken being an extension to that previously presented by Brammer (2002). Three fire scenarios are considered, each having been a real test fire undertaken at the Building Research Establishment in Cardington. These three fire scenarios all involved the flaming combustion of an upholstered armchair within the lounge on the Ground floor. During the experiments various results were recorded, including temperatures, optical densities and smoke detector activation times. The fire scenarios where modelled using FDS, Version 5. Base parameters regarding the fuel load where defined to be 0.05kgsoot/kgfuel and 20MJ/kg. Consideration was also given to the effect varying the effective heat of combustion and defined soot yield would have on derived smoke detector activation times. Additional simulations where thus run considering soot yields of 0.04kgsoot/kgfuel and 0.10ksoot/kgfuel, and an effective heat of combustion of 25MJ/kg. Three prediction methods where applied to the results of the FDS simulations for derivation of the activation times of smoke detectors located throughout the house. These methods where the temperature correlation method, Heskestad’s method, and Cleary’s method. The temperature correlation method considered activation criterions of 4°C, 13°C and 20°C above ambient. The Heskestad and Cleary methods were found to derive comparable activation times for each detector location. None of the prediction algorithms where however found to predict activation times consistently comparable to the test data. Rather, it was determined that for an appropriate prediction method to be adopted for accurate assessment of a given fire scenario, consideration must be given to the: • type of detector being assessed; • location of the detector relative to the fire; • mode of combustion (i.e. flaming or smouldering); and the • growth rate of the fire.

Post-fire reconstruction often includes the analysis of smoke alarms. The determination of whether or not an alarm has sounded during a fire event is of great interest. Until recently, analysis of smoke alarms involved in fires has been limited to electrical diagnostics, which, at best, determined whether or not a smoke alarm was capable of alarm during the fire event. It has subsequently been proposed that evaluation of the soot deposition around a smoke alarm horn can be used to conclude whether a smoke alarm has sounded during a fire event. In order to evaluate the effectiveness of using enhanced soot deposition patterns as an indication of smoke alarms sounding within a fire event, four test series were undertaken. First, a population of smoke alarms representative of the available market variety of horn configurations was selected. This population was subjected four test series. Test Series 1 consisted of UL/EN style experiments with fuel sources that included flaming polyurethane, smoldering polyurethane, flaming wood crib, and flaming turpentine pool. In Test Series 2, alarms were exposed to "nuisance" products from frying bacon, frying tortillas, burnt toast, frying breading, and airborne dust. Test Series 3 exposed the alarms to the following fire sources: smoldering cable, flaming cable, flaming boxes with paper, and flaming boxes with plastic cups. Test Series 4 included new, used, and pre-exposed smoke alarms that were exposed to two larger scale fires: a smoldering transitioning to flaming cabinet/wall assembly fire and a flaming couch section. The results from all four series were used to generate a hueristic for use in evaluating alarms from fire events. These criteria were blindly tested against the population of alarms to develop a correlation between the criteria and the previously tested smoke alarms. The results support the evaluation of soot deposition on smoke alarms exposed to a fire event as a viable method to determine whether or not an alarm sounded, without false positive or negative identifications.

Every year, approximately 100 people die in fire related incidents in Sweden. ”Seek” is designed to assist fire fighters to locate people faster in smoke diving procedures. ”Seek” identifies people and possible dangers within the building before the smoke diving procedure begins. This allows the operation to be streamlined and planned, as well as avoiding risks which fire fighters are exposed to today. The early overview created by the ”Seek” smoke detector not only saves time in planning but reduces the time from accident until the people in the burning building can receive skilled care, increasing their chance of survival.

Det här projektet har utforskat frågeställningen - Hur kan en brand- varnare utformas för att bli mer estetiskt tilltalande för användaren? Den svenska Myndigheten för Samhällsskydd och Beredskap [MSB] har länge drivit en nollvision för Sverige med målsättningen att ingen människa ska omkomma i en brand (MSB, 2021a). En avgörande faktor för att målsättningen ska lyckas är att varje hem har fungerande brandvarnare. Med fungerande brandvarnare i alla hem skulle så många som 40% av dödsfallen kunna förhindras (Runefors, Johansson & van Hees, 2016). Studien genomfördes utifrån ett användar-centrerat arbetssätt där kvalitativa intervjuer med fem informanter samt krav från den europeiska standarden för utformning av brandvarnare har legat till grund för för arbetets utveckling. Intervjuerna visade att informanterna till stor del var negativt inställda till utformningen av existerande brandvarnare då de uppfattades som billiga puckar i vit plast. Det framkom att lågt pris, liten storlek och enkel montering utan borrning var de viktigaste egenskaperna för användarna. De uppgav även att de ogillade att byta batterier samt efterfrågade möjlighet till ökat visuellt samspel med övrig inredning. Naturmaterial och mjuka former var de mest efterfrågade egenskaperna för utformningen. Det kunskapsmässiga bidraget ligger i upptäckten av svårigheterna att samtala om Estetik med informanterna. Detta var en förtydligande insikt över skillnaderna mellan det akademiska och det allmänna språkbruket för att beskriva estetiska intryck. Resultatet av projektet blev en liten brandvarnare med en kropp i massivt trä, en stor knapp för testning och tystande av larm samt en batteritid på minst 10 år. / This project have explored the question - How can a smoke alarm be designed to be more aesthetically pleasing for the user? The Swedish Agency for Civil Protection and Emergency Planning [MSB] has long pursued a zero vision for Sweden with the goal that no one should die in a fire (MSB, 2021a). A crucial factor for the goal to succeed is that every home has a functioning smoke alarm. With effective smoke alarms in all homes, as many as 40% of deaths could be prevented (Runefors, Johansson & van Hees, 2016). The study was carried out on the basis of a user-centered approach where qualitative interviews with five informants and requirements from the European standard for the design of smoke alarms have formed the basis for the development of the project. Based on the interviews, it emerged that the informants were largely negative about the design of existing smoke alarms. These were perceived as cheap pucks in white plastic. It turned out that a low price, small size and an easy installation without the need for drilling were the most important features for the users. They also stated that they did not like to change batteries and requested the opportunity for increased visual unity with other furnishings. Natural materials and soft shapes were the most sought after properties for the design. The knowledge contribution lies in the discovery of the difficulties in discussing Aesthetics with the informants. This was a clarifying insight into the differences between academic and general language for describing aesthetic impressions. The result of the project was a small smoke alarm with a body in solid wood, a large button for testing and silencing of the alarm together with a battery life of atleast 10 years.