1,721,026 research outputs found
A simple analytical method for determining the atmospheric dispersion of upward-directed high velocity releases
No full textA simple analytical method for determining the extension and shape of flammable releases from high velocity sources
No full textGeneralized linearization of kinetics of glucose isomerization to fructose by immobilized glucose isomerase
No full textThe kinetic parameters of both glucose isomerization to fructose and immobilized glucose isomerase (GI) inactivation calculated under different conditions are compared and discussed
Linearization of the kinetics of glucose isomerization to fructose by immobilized glucose isomerase
No full textThis study proposes a pseudo-linear model for the kinetics of glucose isomerization to fructose by immobilized glucose isomerase
HazMat transportation by heavy vehicles and road tunnels. A simplified modelling procedure to risk assessment and mitigation applied to an Italian case-study
No full textThere are various factors influencing the occurrence of road accidents, among which mechanical, environmental, behavioural, physical and road intrinsic descriptors may be mentioned. In facing the routing problem, a realistic evaluation of the frequency must take into account on one side inherent parameters and attributes of the road, on the other side factors correlated to traffic. A framework of general applicability is presented and applied to an Italian case-study in order to assess and evaluate the risk connected to dangerous goods transportation by heavy vehicles (HV). Possible restrictions and alternatives connected to re-routing are analyzed, considering in depth the risk for a possible tunnel alternative route. The problem of tunnel option and related accident scenarios for HV are discussed, so to select proper risk mitigation measures, inherent to heavy vehicle and to tunnel. Regarding the last issue, a novel analytical model for solving the ventilation design for both plane and sloping tunnels is presented
Limiting values of the thermal power and flame temperature from hydrocarbon pool fires.
No full textAs well known, risk is a combination of probability and consequences of an accident. Different concepts were developed in evaluating accident consequences. First, the worst-case concept, meaning that the most negative consequences imaginable are described. A more applied approach is the reference to the maximum credible accident scenario. In analyzing the consequence of accidental hydrocarbon fires and the potential for domino effects, the evaluation of the flame extent and temperature are of the utmost importance. The primary effects of pool fires are due to thermal radiation and issues of interplant/tank spacing employees' safety zones, fire wall specifications are to be addressed on the basis of a proper consequence analysis. In order to avoid too conservative results, imposing anti-economic geometric constraints, for example in term of spacing, a realistic scenario evaluation is therefore needed. By means of real scale experimental tests it was verified that both the thermal power and the flame temperature T increase as the pool area increases, up to reach maximum values in connection with a "critical pool dimension". Dealing with pool areas higher than the critical one, experimental results, performed by different researchers at different scales, show a decrease of T. An in-depth analysis of the different concurring phenomena connected to a pool fire development allowed identifying the limiting step controlling the flame temperature In fact, the trend of T is mainly determined by the increasing difficulty of oxygen diffusion within the internal bulk of gaseous hydrocarbons. In this paper, we propose a pool fire model suitable: • to provide a theoretical insight into the above-mentioned experimental trends; • to obtain the maximum values of the flame temperature and of the thermal power, considering the pool size and the chemico-physical characteristics of the hydrocarbon
A study on road tunnel fires using hazmat, with emphasis on critical ventilation velocity
No full textOne of the main protective measures to be adopted in case of fires in road/rail tunnels is represented by suitable longitudinal ventilation systems being able to avoid fire and smoke exposure of humans, and to create a safe route upstream for evacuation. The key design parameter is the so-called critical ventilation velocity, i.e. the minimum speed of the longitudinal ventilation avoiding the spread of the smoke produced by fire in the upstream direction, known as ‘backlayering’. In several studies, the critical velocity was correlated to the fire heat release rate on the basis of semi-empirical models, already adopted in describing nonconfined fires. However, experimental runs both on a laboratory scale and on a real scale, evidenced that such correlations are valid only in connection with fires of limited extent, while at high rates of heat release and when the flame height reaches the tunnel ceiling, the critical velocity can tend asymptotically to a maximum value vca. In this study, reference was made to the worst scenario of hydrocarbon pool fire extended to the whole tunnel section. The main hypotheses the model is based upon are uniform distribution of chemico-physical properties of fire and smoke along the considered transverse section of the tunnel. The evaluation of the critical velocity is performed by solving mass, momentum and energy balances obtained considering possible dynamic interactions among the different fluxes (backlayering, air, flame/smoke column). In particular, the inertial action exerted by fresh air on backlayering was determined on the basis of the experimental results. The asymptotic value of the critical velocity resulting by mathematical modelling is in good agreement with those proposed by other authors, for example by means of complex CFD (computational fluid dynamics) studies. Moreover, the developed model is easily adaptable to the evaluation of vca, when dealing with geometrical conditions different from the ones studied here e.g., tunnel of different geometry, fire not extended to the whole section of the tunnel, obstacle presence in the tunnel, sloping tunnels
A unified short-cut model approach to size safe venting stacks and other blow-off devices for hazardous vapours
No full textStarting from a general model regarding the atmospheric dispersion of upward-directed high velocity releases, a unified short-cut method is developed for properly designing flares, vents and other safety devices for hazardous material releases and/or to verify the adequacy of the existing ones. By comparison with the design constraints arising from the prevention and protection criteria against the risk of ignition, explosion and exposure of people to radiating heat and/or toxic compounds, the proposed procedure directly gives size, height and location of the venting system as a function of significant release characteristics. A way of economical optimisation is also considered in flare design, where raising the emission also increases the safe areas available to workers
A study on road and rail tunnel fires from hazmat, with emphasis on critical ventilation velocity
No full textOne of the main protective measures to be adopted in case of fires in road/rail tunnels
is represented by suitable longitudinal ventilation systems being able to avoid fire
and smoke exposure of humans, and to create a safe route upstream for evacuation.
The key design parameter is the so-called critical ventilation velocity, i.e. the minimum speed
of the longitudinal ventilation avoiding the spread of the smoke produced by fire in the
upstream direction, known as ‘backlayering’. In several studies, the critical velocity was correlated
to the fire heat release rate on the basis of semi-empirical models, already adopted in
describing nonconfined fires. However, experimental runs both on a laboratory scale and on a
real scale, evidenced that such correlations are valid only in connection with fires of limited
extent, while at high rates of heat release and when the flame height reaches the tunnel ceiling,
the critical velocity can tend asymptotically to a maximum value vca. In this study, reference
was made to the worst scenario of hydrocarbon pool fire extended to the whole tunnel section.
The main hypotheses the model is based upon are uniform distribution of chemico-physical
properties of fire and smoke along the considered transverse section of the tunnel. The evaluation
of the critical velocity is performed by solving mass, momentum and energy balances
obtained considering possible dynamic interactions among the different fluxes (backlayering,
air, flame/smoke column). In particular, the inertial action exerted by fresh air on backlayering
was determined on the basis of the experimental results. The asymptotic value of the critical
velocity resulting by mathematical modelling is in good agreement with those proposed by
other authors, for example by means of complex CFD (computational fluid dynamics) studies.
Moreover, the developed model is easily adaptable to the evaluation of vca, when dealing with
geometrical conditions different from the ones studied here e.g., tunnel of different geometry,
fire not extended to the whole section of the tunnel, obstacle presence in the tunnel, sloping
tunnels
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