Determining of an ideal edge radius of kindergarten furniture for the minimization of injury risks in the event of head collisions

Status:

completed 06/2019

Aims:

Falls against edges of furniture in children's daycare facilities are a significant form of accident causing serious injuries. In order for the existing recommendations for the specific edge design made in DGUV Rule 102-002 governing children's daycare facilities to be revised, better empirical data serving as a reference are required. The recommendations currently applied (edge radius ≥ 2 mm) lack the requisite scientific basis, and are repeatedly challenged, particularly by the manufacturers of kindergarten furniture. The focus lies upon accidents involving children aged three, who constitute the upper limit of the under-threes age group. An empirical study of the collision strain was to be performed for a typical accident scenario (fall). Certain factors influencing the severity of injury (e.g. collision points and collision velocity of the head) were to be varied in consideration of the situation in practice. The biomechanical and physical stress variables, in the form of the collision forces and pressures and the kinematic variables of the masses of the body model, were to be measured and evaluated. With reference to the resulting data, analyses and comparable evaluations were to be used to formulate specific safety requirements for the design of the furniture edges. At the same time, relevant medical expertise was to be exploited concerning probable injuries based upon the measured and interpreted values.

Activities/Methods:

In the study method employed, the accident scenario was simulated with recording of the stress criteria by means of dynamic structural analysis employing finite-element (FE) analysis. The fall type selected assumed a child who tripped, for example on a floor edge, whilst running and fell, striking its head on the edge of the furniture. The first step of the studies was to determine typical walking and running velocities of children in the under-threes age group under analysis. Measurements were performed for this purpose on a total of 30 children in three children's daycare facilities. Walking and running velocities of 0.25, 1.5 and 2.5 m/s were specified for the FE parameter study. A multimass model of a child's body was generated with coupling of adequate biofidelity. For this purpose, the size and mass distribution and the coupling parameters of the individual bodies were taken from anthropometric atlases and the technical specifications of child dummies. The anatomical FE model was derived from a realistic computed tomography (CT) data collection of a three year-old child's head. This data collection was then converted to CAD data by means of a special software application, suitably meshed for the FE analysis, and assigned the biological strength parameters from the databases available in 2016 (FE head model). The entire data adjustment and FE analysis was performed at CADFEM. The FE analyses were repeated systematically with the specified variations, in particular with different edge radii (of 2, 4, 6, 8 and 10 mm). The analysis model was verified in the laboratory by experimental reconstruction of a collision variant with a standardized child dummy (Q3 – age three years). The stress data from the FE analyses were then also to be evaluated by medical experts with regard to their injury potential.

Results:

The level of stress and strain caused by a head collision is, firstly, a function of the radius of the furniture edge, and secondly directly proportional to the impact velocity and thus to the running and walking velocities of the children. The smaller the edge radius, the greater the pressure and tensile stresses at the body point concerned. The simulation model employed by CADFEM (2016) computed a significant reduction of up to 50% in the maximum pressure and maximum comparative tensile stress in the collision surface at all impact velocities (0.1 to 6 m/s) when the radius was increased from 2 mm to 6 mm or greater. At higher impact velocities, the skull and brain were subjected to greater stresses, as well as the skin. These stresses however are virtually independent of the radius in the simulation, since the pressure is distributed within the deeper body layers. The maximum contact force of approximately 4.5 kN measured in the experiment with the child dummy at an impact velocity of 4.1 m/s confirms the values computed in the simulation study. For educational and organizational reasons, it will not be possible to influence the running velocities of children. This study suggests however that the impacts upon health could be reduced by greater radii in the furniture edges in non-circulation areas. The literature survey revealed only a small number of comparable studies on the subject. In the course of the project, it was found that the simulation models must be refined further in accordance with current scientific knowledge in order for better results to be obtained. The authors recommend that the fundamental question of simulation of contusions/lacerations or haematoma be examined in further research projects.

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