Field Evaluation of CO2 Detector Tubes for Measuring Outdoor Air Supply Rate in the Indoor Environment

Indoor carbon dioxide (CO₂) concentration can be used to estimate the degree of air recirculation and outdoor air supply rate. Three types of CO₂ detector tubes were evaluated by using Fourier Transform Infra-Red (FTIR) Spectroscopy as a reference method. Two types of detector tubes (Draeger CH 30801 and Kitagawa 126 B) showed a good correlation with the reference method (r = 0.98), the 95% confidence interval of the slope being 0.89-1.06 and 0.80-0.95, respectively in linear regression analysis. The third type (Gastec 2LL.) showed lower correlation (r = 0.91) and a wider 95% confidence interval (0.52-0.80) of the slope. A t CO₂ concentrations in the range 800-1000 5 l/l(ppm), control values suggested for the indoor environment, the Draeger and the Gastec tubes underestimated the CO₂ concentration, while the Kitagawa tube showed a correct value. The difference in reading between observers was similar for all three brands of detector tubes (5-7%), expressed as relative standard error No significant influence of the air humidity or temperature on the readings could be demonstrated. It is concluded that some brands of CO₂ detector tubes can be used to measure indoor carbon dioxide concentration with sufficient precision and accuracy. Since the relative error is relatively large at lower CO₂ concentrations, the use of such tubes for the determination of air recirculation in ventilation systems should be avoided. As a crude estimate of the outdoor air supply rate, however, CO₂ detector tubes may be used. In order to minimize the error in reading, the type of detector tube and the need for recalibration should be considered. When using CO₂ measurements as an estimate of outdoor air supply rate, the influence of age and work-load on the individual's emission of CO₂ and the time needed to reach equilibrium, should also be taken into consideration.     

Interpretation and Limitations of the Concept “Total Volatile Organic Compounds” (TVOC) as an Indicator of Human Responses to Exposures of Volatile Organic Compounds (VOC) in Indoor Air

The TVOC summation of masses of non-reactive substances has often been used as a practical way of reporting environmental measurements of volatile organic compounds. This total concentration, moreover, is often used as an indication of the potential of a multiomponent atmospheric pollution with substances of low chemical reactivity to cause chemically induced sensory irritation. This use of the TVOC indicator has never been standardized. Various authors have used different measuring techniques and the results have been used to predict certain types of health effect. This article discusses the toxicological background for the TVOC concept in relation to nonspecific sensory irritation and identifies some theoretical limitations in its use within this context. The TVOC indicator of nonspecific sensory irritations should be based only on a limited range of compounds and should be interpreted as a lower limit of the possible intensity of sensory irritation. Based on the discussions, some precautions are recommended with respect to measurements of TVOC and interpretation of the measurements.     

Numerical integration of partial differential equations using principles of multidimensional wave digital filters

Physical systems described by partial differential equations (PDEs) are usually passive (due to conservation of energy) and furthermore massively parallel and only locally interconnected (due to the principle of action at proximity, as opposed to action at a distance). An approach is developed for numerically integrating such PDEs by means of algorithms that offer massive parallelism and require only local interconnections. These algorithms are based on the principles of multidimensional wave digital filtering and amount to directly simulating the actual physical system by means of a discrete passive dynamical system. They inherit all the good properties known to hold for wave digital filters, in particular the full range of robustness properties typical for these filters.In this paper, only the linear case is considered, with particular emphasis on systems of PDEs of hyperbolic type. The main features are explained by means of an example.     

Self-assessed changes in mental health and employment status as a result of unemployment training

The main question addressed in this article is: What factors in an unemployment programme serve both the individual and society? Our research focuses on background variables and process variables and how these can be assumed to affect certain dependent variables in unemployment training. The current focus is on the dependent variable "subjective assessment of the effect of the training on mental health", together with the more objective dependent variable of "employment status after training". Self-confidence, well-being, faith in the future, level of initiative and personal development have been used as indicators of self-assessed "mental health". Data were collected from an unemployment training programme in Sweden and the variables combined to create a hypothetical model. The model was statistically tested and then modified with the aid of LISREL statistics, which helps to adjust the model to statistical acceptance. The findings show that the salient factors directly related to the subjective assessment of the effect of training on mental health are gender, attitude to skills development, perceived training requirements and formal educational background. The latter relationship was negative. Of indirect importance are the level of commitment of the teacher, the satisfaction of the trainee with the process, and the level of control. The duration of previous unemployment was the only independent variable, which directly affected the employment status after the training, and this was in the negative direction. Of indirect importance for this dependent variable were training requirement, satisfaction with the process, own level of control and attitude to skills development.     

Analytical approaches to improved characterization of substitution in hydroxypropyl cellulose

Chemical characterization of cellulose derivatives is of high importance as it provides information about the often inhomogeneous substitution that may seriously affect the properties of these polymers in various applications. A detailed mapping of the chemical structure of these derivatives requires several advanced techniques to be employed. In this study, the average substitution and the substitution heterogeneity in two hydroxypropyl cellulose (HPC) samples from different suppliers were studied by means of NMR spectroscopy, MALDI-TOF MS, and HPAEC-PAD. (1)H and (13)C NMR provided information on the molar substitution, a parameter that could be analyzed by MALDI-TOF MS as well. In addition, the latter technique was used for determination of the distribution of the number of hydroxypropyl groups per glucose unit present in the two polymers. The heterogeneity of the substitution was studied by determining the amount of unsubstituted glucose units in the HPC samples, which was accomplished by HPAEC-PAD analysis. The results obtained suggest that the two HPC samples differ in both hydroxypropoxy content and distribution of the hydroxypropyl groups. Further, the benefits and importance of employing several analytical methods when investigating the cellulose ether substitution are demonstrated, as each method provides different kinds of information on the chemical content.     

Exploration and taxation: Some normative issues

The paper is concerned with a model for optimal search developed by Weitzman [4]. This model is applied to show that the Norwegian system of tax and regulation on exploratory effort may distort the optimal order of search.     

Chemical and Biological Evaluation of Building Material Emissions

Abstract The impact on air quality of the emission of pollutants from freshly conditioned sealant and waterborne paint, and a new carpet was investigated by means of a closed emission system and a high loading factor, i.e. “maximized” test conditions. VOCs were measured. Speciated TVOC values obtained by summation of single VOCs and TVOC (cyclohexane equivalents) values determined by IR spectroscopy were of the same order of magnitude for the carpet and for the sealant. Biological evaluation of the effects of the VOCs was undertaken from the concentrations and the odour and irritation thresholds of each substance. The overall agreements and the mutual supplementation of the results from the TVOC and biological evaluations were apparent, suggesting that both approaches should be part of the evaluation of emissions from building materials. Also the mouse bioassay ( ASTM, 1984 ) was used for evaluation of the irritants emitted. Chemical emission testing and the use of established lists of irritation thresholds appear to be more cost-effective, due to the low sensitivity of the bioassay. This approach was demonstrated with 2-butanone oxime (emitted from the sealant). The same type of approach may be used in relation to odour and hazard identification. However, human and animal tests are necessary in cases where biological data are lacking or where the chemical emission is unknown.