Steady-state tube furnace

Recently, two significant developments have raised the profile of fire toxicity. The first is the development of the steady-state tube furnace (SSTF) (ISO TS 19700 2006), which has been shown to replicate the toxic product yields corresponding to the individual stages of fires. The second is the acceptance of performance-based fire design as an alternative to prescriptive fire regulations, so that architects can specify the components within a building based on a safe escape time, within which toxic and irritant gas concentrations must not approach a lethal level (ISO 13571 2007). 

Steady state tube furnace O ISO room O 1/3 ISO room Cone calorimeter... 

The fire toxicity of each material has been measured under different fire conditions. The influence of polymer nanocomposite formation and fire retardants on the yields of toxic products from fire is studied using the ISO 19700 steady-state tube furnace, and it is found that under early stages of burning more carbon monoxide may be formed in the presence of nanofillers and fire retardants, but under the more toxic under-ventilated conditions, less toxic products are formed. Carbon monoxide yields were measured, together with HCN, nitric acid (NO), and nitrogen dioxide (NO2) yields for PA6 materials, for a series of characteristic fire types from well-ventilated to large vitiated. The yields are all expressed on a mass loss basis. 

Fig. 4.4. Stages in zone refining o bar of impure silicon (a) We start with a bar that has a uniform concentration of impurity, Q. (b) The left-hand end of the bar is melted by o small electric tube furnace, making a liquid zone. The bar is encapsulated in a ceramic tube to stop the liquid running away. ( ) The furnace is moved off to the right, pulling the zone with it. (d) As the zone moves, it takes in more impurity from the melted solid on the right than it leaves behind in the freshly frozen solid on the left. The surplus pushes up the concentration of impurity in the zone, which in turn pushes up the concentration of impurity in the next layer of solid frozen from it. (e) Eventually we reach steady state, (f) When the zone gets to the end of the bar the concentrations in both solid and liquid increase rapidly, (g) How we set up eqn. (4.1).

Figure 3.22 illustrates a process in which steam is introduced through a porous tube into a reactive process stream. Steam is introduced into the closed-end annular region from one end. At steady state all the steam that enters the annular region must flow through the porous wall into the process stream. Assume that the entire system is within a furnace that maintaines a uniform temperature. The inner radius of the process tube is rt, and the inner and outer radii of the annulus are r, and rQ, respectively. Overall, the system has an axial length L. The mass-flow rates of the steam and process streams are set at ms and mt, respectively. 

A tube furnace drawn over the mullite outer casing is used to heat the contents to a specified temperature, based on a furnace control thermocouple. At the same time, a constant ac voltage2 is applied across the central heater. The microprocessor waits until temperature fluctuations (within 0.1°C, over one minute) at any of the inside or outside thermocouples are eliminated.3 At that point, steady state conditions are assumed to exist. 

The Freeh two-step furnace, with separate control of the vaporization and atomization functions, represents a substantial improvement on commercial Massmann-type and THGA furnaces for interference-free analyses by ETA-AAS. However, it has the disadvantage that it relies on diffusion and convection to transport sample vapours from the cup vaporizer to the tube atomizer. Transport by purging is one solution to this shortcoming. For this purpose, the Massmann-type atomizer is heated to a steady-state atomization temperature and the THGA vaporizer is pulse-heated to have the purge gas drive the analyte from the vaporizer to the atomizer [21],... 

A test protocol has recently been published in which the toxic potency of fire gases is determined for different fire models. The test is based on a tube furnace, and the air flow, temperature, and rate of sample introduction are controlled to give steady state burning at predetermined fire models, e,g developing fire, developed, low ventilation developed high temperature fire, etc. This is important since the toxic potency of materials can vary with different fire scenarios (Purser et al.) [2]. 

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