This study investigates the effects of different treatments on the flame retardancy of wood,with the aim of identifying which sample types are most suitable for use in construction. Fourtypes of pine wood samples were examined: untreated, densified, flame-retardant-treated, andboth densified and flame-retardant-treated.

Fires remain a significant safety concern in Sweden, with approximately 10 500 incidentsoccurring annually around half in residential areas resulting in an average of 85 deaths eachyear. As such, improving the fire resistance of commonly used construction materials likepine wood is crucial.

A variety of flame retardants exist, each designed for specific applications. These chemicalsoperate through mechanisms such as cooling the material, forming protective char layers, ordiluting flammable gases. However, some flame retardants may unintentionally increase thematerial's total heat release.

This project focused on a flame-retardant system composed of ammonium dihydrogenphosphate and urea. Upon heating, ammonium dihydrogen phosphate decomposes to releaseammonia and phosphoric acid. The ammonia helps to extinguish flames by releasing noncombustible gases, while the phosphoric acid forms a char layer that insulates the wood andrestricts oxygen access. The combination of urea and phosphate enhances the flameretardant's effectiveness through six synergistic mechanisms.

The study also included densification through thermo-mechanical treatment, a process thatcompresses the wood, closes its pores, and increases its density—thereby limiting internaloxygen and making combustion less likely.

Pine wood was chosen for this experiment due to its widespread use in construction,affordability, and lightweight properties. The fire behaviour of the samples was assessedusing two main methods: Microscale Combustion Calorimetry (MCC) and Cone Calorimetry.In the MCC tests, three sample types; untreated, densified, and flame-retardant-treateddensified wood, were examined. The Cone Calorimeter tested these same samples, plus onethat was only flame-retardant-treated. Each sample was tested three times to ensure accuracy.

Results indicated that flame-retardant-treated wood performed the best in fire resistance,followed by the flame-retardant-treated and densified wood. These findings suggest that flameretardant treatment significantly enhances the fire safety of pine wood. Future studies arerecommended to refine the data and further understand the long-term performance anddurability of flame-retardant-treated wood in construction settings.