In this paper, the influence of sample pressure on benzene measurements obtained with two automated in situ gas chromatographs is studied. The analysers were calibrated using a non-linear regression at 293 ± 1 K and 101.3 ± 0.2 kPa. A gas mixture of benzene in air (5 μg/m) was produced and measured at calibration conditions. Subsequently, the sample pressure was changed to 80 and 110 kPa. Differences in readings were observed even though the pressure compensators were on, indicating incorrect performance of this tool. Further tests with two different benzene in air mixtures (5 and 40 μg/m) at 80, 90, 105 and 110 kPa were also carried out. Results showed that the analysers take air from one or several unidentified inlets (apart from the sampling port) when the sampling pressure is lower than the atmospheric one. This is usually the case in air monitoring stations, so this phenomenon is particularly important as systematic biases could be affecting air quality data.

Abstract. Calibration of in situ analysers of air pollutants is usually done with dry standards. In this paper, the influence of sample temperature and environmental humidity on benzene measurements by gas chromatography coupled with a photoionisation detector (GC-PID) is studied. Two reference gas mixtures (40 and 5 µg m −3 nominal concentration benzene in air) were subjected to two temperature cycles (20/5/20 • C and 20/35/20 • C) and measured with two identical GC-PIDs. The change in sample temperature did not produce any significant change in readings. Regarding ambient humidity, the chromatographs were calibrated for benzene with dry gases and subjected to measure reference standards with humidity (20 and 80 % at 20 • C). When measuring a concentration of 0.5 µg m −3 benzene in air, the levels of humidity tested did not produce any significant interference in measurements taken with any of the analysers. However, when measuring a concentration of 40 µg m −3 , biases in measurements of 18 and 21 % for each respective analyser were obtained when the relative humidity of the sample was 80 % at 20 • C. Further tests were carried out to study the nature of this interference. Results show that humidity interference depends on both the amount fractions of water vapour and benzene. If benzene concentrations in an area are close to its annual limit value (5 µg m −3 ), biases of 2.2 % can be expected when the absolute humidity is 8.6 g cm −3 -corresponding to a relative humidity of 50 % at 20 • C. This can be accounted for in the uncertainty budget of measurements with no need for corrections. If benzene concentrations are above the annual limit value, biases become higher. Thus, in these cases, actions should be taken to reduce the humidity interference, as an underestimation of benzene concentrations may cause a mismanagement of air quality in these situations.

The serious consequences of explosions justify the efforts in prevention. The inherent danger of the phenomenon and the possibility of causing other concatenated accidents (domino effect) can increase the damage. To assess the damage and plan the emergency, it is necessary to determine the possible scope of dangerous magnitudes of the explosion (high pressure, mechanical impulse, and range of the fragments). It is important to consider that the peak overpressure of explosive detonation is relatively high and impulse width short near the source. Both parameters (overpressure and impulse) decrease with the distance but the decrease is not uniform, so that the ratio of contributions of overpressure and impulse to damage of receptors differ. In this work, the TNT equivalence method has been selected to determine the overpressure and impulse of the wave when detonation of high explosives occurs outdoors and the most recognized PROBIT functions to estimate the consequences of such accidents on humans. Combining both methodologies for each type of damage, graphical relationships of the primary parameters were obtained. Previously existing relationships have been parameterized to facilitate its implementation in software and to provide intuitive information to use it in studies of risk analysis of these accidents. © 2015 American Institute of Chemical Engineers Process Saf Prog 35: 233–240, 2016