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Oxygen-enrichment in foam insulation for liquid-nitrogen transfer lines constitutes a potential fire hazard. Measurements of oxygen levels inside two types of foam insulated systems have been earried out. Samples of gas were taken from the innermost part of the foam by means of a syringe, and then transferred to an oxygen sensitive, chemical cell. Oxygen levels above 30 % were detected shortly after start of warming-up in one system. The oxygen percentage decreased at a rate that was dependent on how well the insulation was ventilated through seams etc. A long range effect of oxygen-enrichment can be expected in systems that have been running for some years. A substantial part of the foam will then be affected due to diffusion of oxygen-rich gas into the cells of the foam in combination with a large number of open cells as a result of the thermal cyclings.
oxygen-enrichment, foam insulation, liquid nitrogen, transfer line, fire hazard
project manager, AGA AB Innovation, Lidingö,