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The effects of high-intensity pulsed-light emissions of high or low UV content on the survival of predetermined populations ofListeria monocytogenes, Escherichia coli,Salmonella enteritidis, Pseudomonas aeruginosa,Bacillus cereus, and Staphylococcus aureus were investigated. Bacterial cultures were seeded separately on the surface of tryptone soya-yeast extract agar and were reduced by up to 2 or 6 log10 orders with 200 light pulses (pulse duration, ∼100 ns) of low or high UV content, respectively (P < 0.001).

The effects of high intensity light emissions, produced by a novel pulsed power energization technique (PPET), on the survival of bacterial populations of verocytotoxigenic Escherichia coli (serotype 0157:H7) and Listeria monocytogenes (serotype 4b) were investigated. Using this PPET approach, many megawatts (MW) of peak electrical power were dissipated in the light source in an extremely short energization time (about 1 ms). The light source was subjected to electric field levels greater than could be achieved under conventional continuous operation, which led to a greater production of the shorter bacteriocidal wavelengths of light. In the exposure experiments, pre-determined bacterial populations were spread onto the surface of Trypone Soya Yeast Extract Agar and were then treated to a series of light pulses (spectral range of 200-530 nm) with an exposure time ranging from 1 to 512 ms. While results showed that as few as 64 light pulses of 1 ms duration were required to reduce E. coli 0157:H7 populations by 99·9% and Listeria populations by 99%, the greater the number of light pulses the larger the reduction in cell numbers (P ³ 0·01). Cell populations of E. coli 0157:H7 and Listeria were reduced by as much as 6 and 7 log 10 orders at the upper exposure level of 512 ms, respectively. Survival data revealed that E. coli 0157:H7 was less resistant to the lethal effects of radiation (P ³ 0·01). These studies have shown that pulsed light emissions can significantly reduce populations of E. coli 0157:H7 and L. monocytogenes on exposed surfaces with exposure times which are 4-6 orders of magnitude lower than those required using continuous u.v. light sources.

A defect such as a free metallic particle or stress-raising edge on an electrode could lead to breakdown in a gas insulated substation (GIs), but may be detected by the partial discharges it generates. Of the various detection means available, most success has been achieved with either acoustic transducers to detect sound waves from the discharge, or electrical couplers to pick up the ultra-high-frequency (UHF) signals generated inside the GIS chambers. All new GIs in the UK are fitted with internal couplers for UHF monitoring, and two examples of continuous monitoring schemes on 400 kV GIS at nuclear power stations are described. Further developments, which are already well advanced, include specifying and measuring the coupler characteristics, making use of expert systems to interpret the UHF discharge data, and extending the monitoring system to include the performance of circuit breakers and other equipment.