It is always concerned that if plastic bumpers with conductive primer surface are not properly grounded when they are subjected to electrostatic spray coating, incendiary electrostatic discharges may occur, resulting in explosion and fire. In order to investigate electrostatic phenomena in relation with the electrification of conductive bumpers, we made an experimental set-up consisting of a high-voltage power supply, a digital oscilloscope, a high-sensitive camera, and an ignition probe system. Five bumper samples were subjected to the experiment. It was made clear that the electrostatic potential of an ungrounded bumper will reach a saturation point determined by the onset of corona discharges which occur on edges of the bumper, and there are negative correlation between the surface resistivity of the primer coating and the discharged static charge. As a result of direct ignition test using an explosive mixture of ethylene and air (minimum ignition energy 0.09 mJ), no ignition was observed at the surface voltage less than or equal to 3.0 kV. It is concluded that if it is necessary to give a bumper static charges to check whether the grounding is secured or not, the maximum potential should be 2 kV or smaller, considering a safety margin.

Even if the oxygen concentration before starting of a work is normal, as time passes, the concentration sometimes falls. As prevention against the anoxia-risk, we thought that it was important for the worker to wear a real-time oxygen deficiency indicator because worker can know oxygen deficiency faster. For this reason, I tried to response characteristics tests of simulation on two patterns which are the main causes of asphyxiation. In the oxygen consumption test using a small testing apparatus, no clear difference in oxygen concentration reduction due to difference in temperature or measurement position was observed. On the other hand, in the oxygen-deficient-air experiment using nitrogen gas, the wearable real-time oxygen deficiency indicator put on the ankle and chest were able to detect lowering of oxygen concentration faster than the oxygen deficiency indicator fixed close to the wall side. These results indicated the possibility of reducing an anoxia-risk by wearing a wearable type oximeter appropriate position by the worker.