Thermal Radiation Hazards from Gas Pipeline Rupture Fireballs

Increasing world-wide demand for gas is resulting in an increased network of gas piping which poses potential hazards to the natural and man-made environment in proximity to the pipelines. In this work we report experimental measurements of the thermal radiation levels generated by fireballs from two fullscale, below-ground, natural-gas pipeline ruptures. The tests were carried out at the DNV GL’s Spadeadam Test Site simulating the rupture of a 1219 mm diameter pipe carrying high pressure natural gas (at 13.4 MPa -nominal gauge pressure). The duration of the fireball and the maximum heat fluxes (as high as 70 kW/m2 at 200 m downwind) were well predicted by current simple mathematical models when a reasonable radiative fraction of the total energy release was assumed. The empirical radiant fraction equation adopted by OGP was shown to overpredict the incident heat flux in these tests. In the second test the grass surrounding the test location was ignited and other vegetation showed significant thermal damage. To interpret such data correctly and to evaluate the hazards, to natural and man-made environments, more information is needed on the effects of short exposure times (of the order of a few seconds) to high transient heat fluxes

Development of the Controlled Atmosphere Cone Calorimeter to Simulate Compartment Fires

The cone calorimeter with the controlled atmosphere compartment was used to control the fire air ventilation and to simulate the behaviour of materials in compartment fires, with rich burning under post flashover conditions. The standard cone calorimeter with controlled atmosphere design has to be improved, by compartment wall insulation, to reduce heat losses which reduced the fire temperature. Heat losses from the test section to the water cooled load cell were shown to be significant and the test specimen was insultated from the support. A chimney was added to the cone outlet to enable the measurement of the mean composition of the raw discharge gases. A method was developed for determining the mean gas sample and to prevent back flow of external air. This improved design was used to create under ventilated fires with pine wood where the equivalence ratio was controlled by the air flow into the compartment. These modified procedures for the cone calorimeter greatly extend its usefulness in material testing to conditions close to those encountered in post flashover compartment fires

PVC Sheathed Electrical Cable Fire Smoke Toxicity

The cone calorimeter, under free and restricted ventilation conditions, was used to investigate the toxic emissions from PVC cable fires. Toxic gases were measured using direct high temperature gas sampling from the exit of the cone calorimeter with a short chimney attached to the exit from the electrical cone. Toxic species CO and HCl were identified as a function of time using a heated Gasmet FTIR. The particle number was determined using the Cambustion DMS500 fast response particle sizer with a diluted sample taken from the diluted cone calorimeter exhaust flow at the same location as the optical obscuration smoke meter. The HCl concentrations from the Chlorine in the PVC sheath demonstrated HCl levels well above the LC50 concentration for HCl. The restricted ventilation reduced the peak fire heat release rate and the peak toxicity and HCl occurred later than for free ventilation. The equivalence ratio in the gases from the combustion zone, were both rich at 1.5 for free ventilation and 1.3-1.4 for restricted ventilation. The toxicity results showed the classic phases of compartment fires: growth, steady state burning and then fire decay. After flaming combustion was extinguished, slow char combustion continued with high CO emissions. The particle size distribution showed peak particle number, PN, nuclei mode particles at 10 nm and an accumulation mode at 100 nm. The number of particles at 10 nm for free and restricted ventilation were extremely high and showed that the freely ventilated fires had the highest PN, but later in the fire the restricted ventilation PN were higher. Nano-particle emissions < 50 nm from PVC fires are a health hazard that is currently unrecognized and unregulated

Hazardous Area Classification for Biomass

Operators of facilities using biomass as a fuel must comply with the Dangerous Substances and Explosive Atmospheres Regulations (2002) (DSEAR). A key requirement of this legislation is that areas where a flammable atmosphere could arise are demarcated into zones. Traditional guidance on zoning or Hazardous Area Classification for dusts has not kept up to date with the latest technology and theories on dust explosion science. This project identified a number of key explosion parameters for spruce biomass through experiments carried out using the 1m³ explosion test vessel. It is suggested that given the relatively high lower explosive limit and guidance from recently issued papers that the size of external zones can be extremely small without any compromise in the safety of a system

Experimental investigation of potential confined ignition sources for vapour cloud explosions

Electrical control boxes are prolific on high vapour cloud hazard sites, and in the case of the Buncefield explosion the ignition source was inside such a box that was sited in an emergency pump house building. There has, however, been relatively little previous research into this type of ignition mechanism and its effect on the explosion severity. Commercially available electrical control boxes measuring 600 mm high, 400 mm wide and 250 mm deep were used to explore the pressure development, venting processes and flame characteristics of stoichiometric propane/air explosions using aluminium foil and the supplied doors as vent coverings. In this work, the boxes were empty of their usual contents in order to establish a baseline for the effect of the internal congestion of the boxes. It was found that, in these empty-box tests, the door produced a flat petal shaped flame, which differed drastically from the mushroom flame shape, associated rolling vortex bubble venting traditionally observed with large orifice vented explosions

Particle size emissions from PVC electrical cable fires

Electrical cables are in every building and form a significant part of fire loads and can through electrical faults be the first item burnt in some fires. PVC insulated cables are still quite common in buildings and this work investigates Prysmian PVC cables. Deaths and injuries in fires are dominated by the influence of toxic smoke emissions and most of the work on the hazards of smoke are concerned with the toxic gases such as CO. However, fires are large producers of particulate material at levels over 1000 times that in controlled combustion and there is little knowledge of the role of ultra-fine particles in fires and none at all for electrical cable fires. The cone calorimeter fire material testing equipment was used in the present work, which is an ideal test procedure for particle size measurement, as controlled dilution (100/1) of the fire products occurs which enabled diluted samples to be used for particulate number measurement. The Cambustion DMS500 transient particle size analyser was used to determine the particle size distribution. The cone calorimeter uses a 100mm square test specimen and this was filled with 10 100mm lengths of the PVC cable. The test specimen was on a load cell so that the mass burn rate was determined. The cone calorimeter ignites the specimen using a conical electrical heater that is calibrated to achieve a control radiant heat flux on the test specimen, which was 35 kW/m2 in the present work. The fire occurred in a restricted air supply with an insulated air box around the 100mm square test fire. A chimney on the conical heater exit was used to obtain a raw gas sample for toxic gas analysis using a heated Gasmet FTIR. For gases dilution is undesirable as oxidation of the toxic gases may occur. For particles the chimney temperature was too low for carbon oxidation to be significant. The dilution process also condenses unburned hydrocarbons and carbonyl species, which may form nano aerosols and these may be the source of the 10nm particles measured in the present work. HCl is a major product of PVC fires and hence hydrochloric acid aerosols are likely in the particulate measurements. In previous work of the authors, PVC cable fires were investigated with free ventilation and HCl yields of about 50% were measured with Acrolein at 5% yield and Formaldyhyde at 3%. Thus there are plenty of liquid aerosol possible in the diluted products of PVC fires. The results showed a large nuclei number peak at about 10nm. The coarse particle peak only started after flaming combustion occurred and this was initially at 200nm, which increased to 300nm after 1000s. The 10nm peak was high for the first 200s, then dropped dramatically and slowly reformed later in the fire and at the end of the fire was very high with a low coarse particle peak. The FTIR gas species will be used to speculate on the likely composition of the nanoaerosols as a function of time in the fire

Comparison of explosion characteristics of Colombian and Kellingley coal

Coal continues to be one of the main fuels used for generation of energy in the UK. Despite government’s plans to decarbonise the energy sector in order to meet GHG emission targets, co-firing of coal and biomass is attractive due to the low investment required and since gas prices remain high, the consumption of coal is still considerable in power generation. Pulverised coal has been known to pose explosion risks since the 19th century. The objective of the present work was to compare the explosibility of two coal samples used in UK power stations which potentially can be used co-fired with biomass. Both samples of coal were fully characterised for their chemical composition as well as particle size and morphology. The 1m3 ISO explosion vessel was used to determine the explosion characteristics: deflagration index (Kst), maximum explosion pressure (Pmax) and minimum explosible concentration (MEC). Flame speeds were also measured. The remaining residues after explosion were also analysed. The results were compared to the explosion characteristics of other types of coal available in the literature. Despite the very similar composition of both fuels, the reactivity of Colombian coal was much higher, with a Kst value of 129 barms-1 as opposed to 73 barms-1 for Kellingley coal (Fig.1). There was significant difference between these two coals as the surface area of Colombian coal was 5 times higher than that of Kellingley coal. There was little difference in the elemental composition, but Colombian coal contained more volatiles and less ash. Thus the results indicate a strong impact of particle surface area and volatile content on the reactivity of coal

Smoke Particle Size Distribution in Pine Wood Fires

There is a growing concern about the impact of ultra- fine particulates released from fires on the health of humans in fires and the related environmental pollution. However, there is no requirement to measure particle mass or number from legislated test fires and hence there is minimum information in the literature on this toxic hazard in fires. This work compares particulates generated from freely ventilated and restricted ventilation pine wood fires using the cone calorimeter. The standard cone calorimeter with freely ventilated combustion was modified by adding a discharge pipe to the cone heater that enabled direct fire product sampling from the cone outlet. The controlled atmosphere cone calorimeter was used for the restricted ventilation fire with metered air fed to the enclosure around the test area. Both tests used a radiant heat flux of 35kW/m2. Real-time particulate number and size distribution were measured using the Cambustion DMS 500 particle electrical mobility spectrometer. The particulate size distribution showed a peak of ultra-fine aerosol particles of <100 nm in the early stage of the fire development and then changed to the larger size (100-1000 nm) with a peak of 200 nm as the fire progressed. The restricted ventilation fire generated more particles. There were high numbers of 20 nm particles throughout the fire and these have the greatest health risks. Toxic gases were also measured from the raw exhaust gases using a heated Gasmet FTIR gas analyser

Agricultural Waste Biomass Energy Potential In Pakistan

Pakistan has a major electricity supply problem with urban areas having a very intermittent supply of electricity. The supply gap at periods of high demand is 6 GW. Pakistan has a large agricultural economic sector and produces a substantial amount of waste material that has little current economic use. This work shows that these agricultural wastes are a significant energy resource that could be used to generate electricity using relatively small biomass generator sets that could take all the waste biomass from the surrounding agricultural area. Pakistan currently imports most of the oil used for electricity generation. The cost of this result in high cost electricity and it is shown that bio-electricity could be generated competitively in Pakistan. It was estimated, based on 30% thermal efficiency of electric power generation, that the annual production of crop residues have the potential to generate 76% of the annual electricity requirements of Pakistan. For this to come from agricultural wastes in farmland, transport costs would have to be minimised. It is proposed that a series of about 10MWe plants should be established (which are commercially available) with all farms in about a 10km radius delivering their agricultural solid waste to the plant at the farmers cost with direct payment by the power generator

Biomass Explosion Residue Analysis

On account of its greenhouse gas advantages there is increasing use of pulverized biomass in power generation. However, there is little information on the combustion properties of pulverized biomass and on the explosion hazards they create in the mills, dust conveyor systems and biomass storage silos. This work uses the ISO 1 m3 dust explosion equipment to study the explosion properties and combustion characteristics of pulverized biomass dust clouds. An unreported feature of this apparatus is that in rich concentrations only about half the dust injected is burned in the explosion. This work was undertaken to try to understand, through measuring the mass and composition of the debris at the end of the explosion, why all the pulverized biomass injected did not burn and the consequences for the measured parameters of flame speed, Pmax and Kst. One possible explanation of the results is that the residue material was formed from biomass dust blown ahead of the flame by the explosion induced wind and deposited on the vessel wall, where it was compressed as the pressure increased in the vessel. The flame side underwent flame impingement pyrolysis and the metal side was heated and compressed in the explosion but not burned. This was supported by photographic and pressure decay data that indicated the presence of a “cake” of dust being formed on the wall of the vessel. The results also show that the overpressures remain high for very rich equivalence ratios of up to 6. The reactivity of biomass was higher than coal for the two types of biomass investigated. No rich combustion limit was found. This challenges the general industry assumption that operating in very rich conditions in mills is safe. An explanation is proposed for the high peak pressures under rich conditions