Aim: The objective of the study was a comparative analysis of the mechanical properties of polymer foams used as impact energy absorbers, a component of firefighter helmets manufactured in Poland. The study aimed at evaluating the influence of the properties of new materials on the working safety and comfort of helmet users.
Methodology: The study utilised an expanded polystyrene insert and polyutherane absorbers obtained from Polish firefighter helmets that were manufactured in various years. Compressive strength tests under quasi-static load and at dynamic conditions with regard to elastic deformations were carried out. They reflected both abnormal and normal operational loads. Comfort of use was evaluated indirectly based on Young’s modulus value.
Results: Compressive strength test results for absorptive materials indicated significant differences between studied absorbers both at normal load conditions and in extraordinary situations. Expanded polystyrene foams and foam from AK-06 helmet from 2012 demonstrated a good strength, high energy absorption capacity and high stiffness. The foam from AK-06 helmet from 2007 was observed to have the worst mechanical properties among the studied materials. The material from 2015 indicated a relatively good strength, energy absorption properties and moderate stiffness.
Conclusions: A variety of absorptive materials with different mechanical properties are used in the structure of firefighter helmets. Laboratory studies allow the selection of the most optimum solution. In the studied firefighter helmets, expanded polystyrene absorptive materials had been replaced by polyurethane. The polyurethane foams applied in helmets manufactured in 2007 were characterized by lower stiffness and inferior properties as compared to inserts made of expanded polystyrene. Later the properties of materials have been improved. However, it was achieved through a significant increase in stiffness with regard to elastic deformations. It seems that the optimum properties among the studied absorbers were achieved by the newest material, which was used in Calisia Vulcan CV 102 helmets from 2015.
Keywords: firefighter helmet, polymer foams, energy absorber, mechanical properties
Type of article: original scientific article