Average mass loss rate

Toxic potency of smoke data can be used as one of the inputs in fire hazard assessment. In particular, they can be combined with average mass loss rates and times to ignition to obtain a quick estimate of toxic fire hazard. 

A vertical slab of PMMA bums in air at an average mass loss rate of 15 g/m2 s. The air temperature is 20 °C. Assume that the heat transfer coefficient of the slab is 15 W/m2 K. Determine the net radiative heat flux to the surface. What amount comes from the flame ... 

It leads to more extreme surface compositions in WC stars, i.e. to smaller surface helium concentrations but higher C- and O-abundances, The surface helium mass fraction Y can be roughly estimated to be larger than a certain value, depending on the mass of the convective core Mcc Y > (Mwc — Mcc)/ Mwc VHe), where Mwc is the mass of the WC star, Mwc its average mass loss rate, and rne its He-burning lifetime. 

Note rign = time to ignition, PHRR = peak of heat release rate, THR = total heat release, AMLR = average mass loss rate, ASEA = average specific extinction area. 

Cone calorimetry was used to measure the effectiveness of the additives on reducing the flammability of PE the parameters available include the heat release rate and especially its peak value, the peak heat release rate (PHRR) and time to peak heat release rate (tPHHR) total heat release (THR) time to ignition (tig) average mass loss rate (AMLR) and average specific extinction area (ASEA), a measure of smoke formation. A decrease in the PHRR, THR, AMLR, and ASEA are desired along with an increase in tig and tPHRR. The heat release rate (HRR) curves as a function of time for pure PE and its nanocomposites are shown in Figure 4A and cone data are summarized in Table II. 

Smoke production rate A product of the average mass loss rate and the average specific extinction area m 7s... 

Results are shown in Table 2.5. All additives were effective in reducing peak HRR to some extent. Of the additives studied ATH (sample 1196) shows 20% and 25% decreases in peak HRR at radiant heat fluxes at 50 and 75 kW/m, respectively, and 24% and 13% decreases in average HRR at 50 and 75 kW/m respectively. Also, average mass loss rates were decreased by 27% and 24% at 50 and 75 kW/m. ... 

A comparison of the combustion properties of EPDM composites containing wet ground and precipitated ATH (Table 17.4) shows significant differences. It is likely that the lower average heat release rate (HRR) and average mass loss rate for the wet... 

The average rate of mass loss is calculated from the amount of mass lost and the corresponding time period. The calculations in Table I at 573 K represent the average mass loss of isothermal dehydrochlorination. Thus, the values in Table I (3.4 %/min for blue conduit, 2.9 %/min for grey conduit and 2.3 %/min for wire coating) represent a reasonable estimate of the mass loss rate of the PVC products in a fire, at a temperature not exceeding 563 K. 

Aho [8] presented a short descriptive model of the relationship between combustion heat rate and mass loss rate of bed. He applies the same method as Koistinen et al [7]. It is clear that the method used presents time average values of combustion heat rate. No verification method is applied and no uncertainty analysis is carried out. The... 

The mass loss rate is determined as the slope of the bed weight curve. It is obtained as a time average value. 

The average heat of combustion is determined from the ratio of the energy, E,-, obtained from the summation of the chemical, convective, and radiative heat release rates and the total mass of gasified polymer, Wf, obtained from the summation of the mass loss rate ... 

Volatilization. Even though the vapor pressure of PCBs is very low, small amounts of spilled PCBs will slowly evaporate into the overlying air (evaporation rate is about 4.8 x 10 to 7.8 X 10 g/m /h) (NRC, 1979). This can happen for spills on both water and soils. Calculations of average mass losses through evaporation could be computed for many spills. As for PCB mixtures that contain chlorobenzenes and mineral oils, the lighter components consisting mainly of chlorobenzenes and mineral oils will evaporate first, leaving behind the thicker PCBs. The evaporation rate is dependent on the wind speed and temperature. However, the net result of volatilization is the removal or transference of PCBs from one environmental compartment to another without any net loss from the environment. 

Table 1. Onset Decomposition (Td), Peak Mass Loss Rate (Tp), and ignition (Tign) Temperatures of Poiymers (Average Vaiues 10°C)...

Heat flux, 35 kW/m. He, specific heat of combustion SEA, specific extinction area g , ignition time. Peak heat release rale, mass loss rate, and SEA data are reproducible to within 10%. The heat of combustion and the time to ignition data are reproducible to within 15%. The cone data reported are the average of three repheated samples. The samples are square plates 100 mm large and 8 mm thick. 

A typical heat release rate curve for a neat epoxy system and the respective layered silicate nanocomposite, is shown in Fig. 2.12. Both peak and average heat release rate, as well as mass loss rates, are all significantly improved through the incorporation of the nanopartieles. In addition, no increase in specific extinction area (soot), CO yields or heat of combustion is noticeable. However, the mechanism of improved flame retardation is still not clear and no general agreement exists as to whether the intercalated or exfoliated structure leads to a better outcome. The reduced mass loss rate occurs only after the sample surface is partially covered with char. The major benefits of the use of layered silicates as a flame retardation additive is that the filler is more environmentally-friendly compared to the commonly used flame retardants and often improves other properties of the material at the same time. However, whilst the layered silicate strategy is not sufficient to meet the strict requirements for most of its application in the electrical and transportation industry, the use of layered silicates for improved flammability performance may allow the removal of a significant portion of conventional flame retardants. 

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