History of Dutch process equipment failure frequencies and the Purple Book

In the middle of 70s concerns of the public in the Netherlands about fire, explosion and toxic risks due to mishaps in the expanding process industry, causing political pressure led to the embracement of quantitative risk analysis as tool for licensing and land-use planning. Probabilistic treatment of risk had been exercised before to design flood defense. A ‘test’ on six different plants, the COVO study, favored the idea. Failure rate values were in immediate need. For storage vessels AKZO’s chlorine vessel data and British steam boiler data have been the first. Risk criteria to make decisions on were also developed and in 1985 embodied in legislation. As licensing and land-use planning are tasks of provincial authorities, under the auspices of the Inter-Provincial Consultation (IPO), further details such as failure frequency values have been worked out. In the late 90s the Purple Book consolidated the information as a guideline for Dutch quantitative risk assessment of process installations.The paper will give a condensed historical overview, guidance to published papers; it will further make comments, explain policy backgrounds, present comparison with other data and will briefly indicate in which direction developments should go to improve QRA.     

Scattering cross-section emission factors for visibility and radiative transfer applications: military vehicles traveling on unpaved roads

Emission factors for particulate matter (PM) are generally reported as mass emission factors (PM mass emitted per time or activity) as appropriate for air quality standards based on mass concentration. However, for visibility and radiative transfer applications, scattering, absorption, and extinction coefficients are the parameters of interest, with visibility standards based on extinction coefficients. These coefficients (dimension of inverse distance) equal cross-section concentrations, and, therefore, cross-section emission factors are appropriate. Scattering cross-section emission factors were determined for dust entrainment by nine vehicles, ranging from light passenger vehicles to heavy military vehicles, traveling on an unpaved road. Each vehicle made multiple passes at multiple speeds while scattering and absorption coefficients, wind velocity and dust plume profiles, and additional parameters were measured downwind of the road. Light absorption of the entrained PM was negligible, and the light extinction was primarily caused by scattering. The resulting scattering cross-section emission factors per vehicle kilometer traveled (vkt) range from 12.5 m2/vkt for a slow (16 km/ hr), light (1176 kg) vehicle to 3724 m2/vkt for a fast (64 km/hr), heavy (17,727 kg) vehicle and generally increase with vehicle speed and mass. The increase is approximately linear with speed, yielding emission factors per vkt and speed ranging from 4.2 m2/(vkt km/hr) to 53 m2/(vkt km/hr). These emission factors depend approximately linearly on vehicle mass within the groups of light (vehicle mass < or =3100 kg) and heavy (vehicle mass >8000 kg) vehicles yielding emission factors per vkt, speed, and mass of 0.0056 m2/(vkt km/hr kg) and 0.0024 m2/(vkt km/hr kg), respectively. Comparison of the scattering cross-section and PM mass emission factors yields average mass scattering efficiencies of 1.5 m2/g for the light vehicles and of 0.8 m2/g for the heavy vehicles indicating that the heavy vehicles entrain larger particles than the light vehicles.     

Temperature, Salinity, and Fluorescence in Southern North Sea: High-Resolution Data Sampled from a Ferry

/ In 1991 and 1992, temperature, salinity, and fluorescence were measured by automatic continuous registration using instrumentation on a ferry crossing the southern North Sea daily along a transect between Zeebrugge, Belgium, and Hull, United Kingdom. The temperature ranged between 4 and 21 degrees C off the Belgian coast and between 6 and 17 degrees C in the middle of the transect. Salinity varied between 34 and 35.5 PSU in the offshore part of the transect, but showed much larger variation along the Belgian and UK estuarine coasts. Fluorescence, which was used as a measure of phytoplankton biomass, was highest at the continental coast and lowest near the English coast. Spring blooms of phytoplankton were found along the continental coast and in the channel-influenced water; in 1991 the blooms were denser than in 1992. Some summer blooms were also recorded. Water masses could be distinguished on the basis of salinity and fluorescence patterns. The general patterns in the data are compared with the literature and discussed in relation to river discharge, light penetration, and wind speed and direction. Finally, the value of automatic and frequent measurements of fluorescence for monitoring phytoplankton is compared with less frequent observations at selected stations. It is concluded that accurate information about phytoplankton biomass can only be established from the high-frequency data. KEY WORDS: Monitoring; Sampling; North Sea; Ferry; Fluorescence; Salinity; Temperature     

Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba

The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18–30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6–12 μmol cm⁻³ sponge day⁻¹. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm⁻³ sponge day⁻¹, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.