Fluorinated halon replacement agents in explosion inerting

The US Federal Aviation Administration (FAA) observed during explosion tests that at a low concentration of agent, some candidate halon replacement agents increased the explosion severity instead of mitigating the event. At UTC Aerospace Systems a test program was developed to assess the behaviour of alternative agents at values below inerting concentration. Two agents were selected, C2HF5 (Penta- fluoroethane, HFC-125) and C6F12O (FK-5-1-12, Novec™1230). Baseline tests were performed with unsuppressed C3H8 (propane)/air mixtures and C3H8/air mixtures with CF3Br (Halon 1301) and N2 (nitrogen). Using CF3Br or N2 at below inerting concentrations mitigated the explosion. C2HF5 was tested against C3H8 at stoichiometric (4 vol%) and lower explosion limit (LEL) (2 vol%). Against 4 vol% C3H8 the combustion was mitigated, proportional to agent concentration; however, low concentrations of C2HF5 with 2 vol% C3H8 enhanced the explosion. Tests with N2 against a volatile mixture of C3H8 with C2HF5 showed that N2 mitigated the events. Final tests were performed with low concentrations of C6F12O against C3H8/air mixtures. This showed similar behaviour to that observed with the C2HF5 tests. Normally during qualification tests for new agents the stoichiometric concentration of a fuel is deemed to be the worst case scenario and the baseline against which agents are tested. The above described test results show that this assumption may need to be reconsidered. This work shows that contrary to common assumption the agents investigated are unlikely to have acted chemically at the flame front, but most likely, mainly cooled the flame and changed the stoichiometry, i.e. the ratio of components of the flammable mixture

The Leeds Evaluation of Efficacy of Detoxification Study (LEEDS) project: An open-label pragmatic randomised control trial comparing the efficacy of differing therapeutic agents for primary care detoxification from either street heroin or methadone [ISRCTN07752728]

BACKGROUND: Heroin is a synthetic opioid with an extensive illicit market leading to large numbers of people becoming addicted. Heroin users often present to community treatment services requesting detoxification and in the UK various agents are used to control symptoms of withdrawal. Dissatisfaction with methadone detoxification [8] has lead to the use of clonidine, lofexidine, buprenorphine and dihydrocodeine; however, there remains limited evaluative research. In Leeds, a city of 700,000 people in the North of England, dihydrocodeine is the detoxification agent of choice. Sublingual buprenorphine, however, is being introduced. The comparative value of these two drugs for helping people successfully and comfortably withdraw from heroin has never been compared in a randomised trial. Additionally, there is a paucity of research evaluating interventions among drug users in the primary care setting. This study seeks to address this by randomising drug users presenting in primary care to receive either dihydrocodeine or buprenorphine. METHODS/DESIGN: The Leeds Evaluation of Efficacy of Detoxification Study (LEEDS) project is a pragmatic randomised trial which will compare the open use of buprenorphine with dihydrocodeine for illicit opiate detoxification, in the UK primary care setting. The LEEDS project will involve consenting adults and will be run in specialist general practice surgeries throughout Leeds. The primary outcome will be the results of a urine opiate screening at the end of the detoxification regimen. Adverse effects and limited data to three and six months will be acquired

Experimental study of radiative heat transfer in a translucent fuel sample exposed to different spectral sources

Radiative heat transfer to a solid is a key mechanism in fire dynamics, and in-depth absorption is especially of importance for translucent fuels. The sample-heater interaction for radiative heat transfer is experimentally investigated in this study with two different heaters (electric resistance and tungsten lamp) using clear PolyMethylMethAcrylate (PMMA) samples from two different formulations (Plexiglass and Lucite). First, the significant effects of the heater type and operating temperature on the radiative heat transfer are revealed with broadband measurements of transmittance on samples of different thicknesses. Then, the attenuation coefficient in Beer-Lambert's law has been calculated from detailed spectral measurements over the full wavelength range encountered in real fires. The measurements present large spectral heterogeneity. These experimental results and calculation of in-depth absorption are used to explain the reason behind the apparent variation of the fuel absorbance with the sample thickness observed in past studies. The measurement of the spectral intensity emitted by the heaters verifies that the common assumption of blackbody behavior is correct for the electric resistance, whereas the tungsten lamp does not even behave as a greybody. This investigation proofs the necessity of a multi-band radiation model to calculate accurately the fire radiative heat transfer which affects directly the in-depth temperature profiles and hence the pyrolysis process for translucent fuel