Abstract:

Objective The fire-fighting protective clothing suspenders are adopted to fix and tighten the protective clothing pants, and have a restrictive effect on the shoulder activities when wearing. Under the premise of ensuring safety and protection, a reasonable and optimized design of the suspenders and a comparison between the original and the optimized suspenders were carried out through objective experiments and subjective evaluation so as to improve the overall ergonomics of the fire-fighting protective clothing, reduce firefighters' occupational injuries and improve their work efficiency.

Method A field survey and questionnaire were conducted. According to the actual needs of firefighters, three optimized suspender designs, i.e. H-shape, X-shape and Y-shape, were proposed. Through objective three-dimensional motion capture experiments and subjective feeling experiments, the scores of maximum shoulder joint movement angle under four movements, movement efficiency of arm flexion and extension and outreach, activity flexibility and comfort of 11 subjects were obtained, and their advantages and disadvantages were comprehensively analyzed and discussed.

Results The features of the innovative design of the fire-fighting protective clothing suspenders are summarized (Tab. 2). Style 1 was an H-shaped suspender that incorporates a carabiner and vest-style design, style 2 an X-shaped suspender with a large piece of fabric to hold the cross-webbing, and style 3 a Y-shaped suspender with a single design on the back. The results of the maximum shoulder joint movement angles are summarized (Tab. 4), and it is clear that any of the suspenders would limit the subject's shoulder joint movement. For each movement, style 1 showed the best mobility and style 2 followed. For style 3, the maximum shoulder joint movement angle during arm flexion and extension and outreach was not significantly different from the original style, while the movement angle was smaller than the original model during walking at constant speed and running at constant speed. The time required for the subjects to wear the various suspenders and complete the specified movements was tested. The results showed that there was a difference in the efficiency of the subjects in completing the specified movements wearing the four suspenders, in the sequence (from high to low) of style 1, style 2, style 3 and the original style, and the unit movement time of the optimal style 1 was 12.39% and 14.60% shorter in arm flexion and extension and outreach, respectively, compared with the original style. The scores of subjective flexibility and comfort are summarized (Tab. 7). From the subjective scores, the subjects' evaluations of upper limb flexibility were consistent with the objective experimental results. In terms of subjective comfort, style 1 and style 2 were significantly better than the original style and style 3. In the experiment, the subjects were asked to evaluate the subjective comfort of four specific parts-neck, shoulder, chest and back (Fig. 5). The results showed that adding elastic fabric could improve the comfort of the shoulder, but on the other hand, the fabric stitching area was too high, which might cause discomfort to the neck. While the style of the suspenders has little effect on the comfort of the chest, the double root design on the back is still a better choice. Overall, all three improved suspenders have merits, and style 1 shows the highest flexibility and comfort.

Conclusion In summary, H-type style 1 has the best effect, both from subjects' upper limb mobility is effectively improved and better than X-shaped style 2 and Y-shaped style 3, the fire-fighting protective clothing suspenders have restrictions on shoulder joint movement, adding elastic fabric in it can weaken this restriction, disperse the shoulder and back pressure, and improve the movement efficiency and subjective comfort, and double root design on the back shows better mobility and comfort compared with the single root. This paper proposes innovative designs for fire-fighting protective clothing suspenders and applies objective methods to evaluate the ergonomics of these suspenders and analyze the influences of different suspenders configurations on upper limb mobility. This paper is expected to provide a reference for the optimal design and evaluation of fire-fighting protective clothing suspenders to improve the wearing performance of fire-fighting protective clothing. The follow-up study should consider a variety of factors such as limb mobility and hygrothermal comfort, and study the materials of fabrics, application parts, and the width of suspenders.

Key words: fire-fighting protective clothing, clothing design, suspender, three-dimensional motion capture, shoulder joint movement angle, subjective evaluation