Carbon Monoxide Migration Research Articles

Study on CO migration characteristics and hazard potential function under ventilation after roof cutting blasting

Multiple toxic gases, such as carbon monoxide (CO), are generated by roof-cutting blasting (RCB) in the automatically formed roadway without coal pillars (AFRCP). To eliminate potential hazards in time, a ventilation model was established based on field data from Dianping Coal Mine. The spatial and temporal evolution characteristics of CO under different conditions after roof-cutting by shaped-charge blasting (SCB) and shaped-charge hydraulic blasting (SCHB), respectively, were investigated by using the Computational Fluid Dynamics (CFD) method. The results demonstrate that the CO gas cloud presents the coupling effect of movement and dilution under ventilation. The charge mainly affects the peak value of CO concentration (PVC). The air velocity affects the PVC and the CO gas cloud's over-limit time (OLT) and migration velocity. Roadway cross-sectional area and corner structure affect the PVC by influencing local air velocity. The CO hazard potential functions of the roadway after RCB were established, indicating a Gaussian-like distribution. The maximum hazard potential of SCHB was found to be 60% lower than that of SCB, and the re-entry time for personnel reduced by 36%. This study can serve as a guide for optimizing the ventilation design of roadways after RCB and contribute to the promotion of AFRCP.

Improving Household Safety via a Dynamic Air Terminal Device in Order to Decrease Carbon Monoxide Migration from a Gas Furnace.

The airtightness of buildings is continuing to grow and impact the indoor environment. Its aim is to conserve energy, but this may influence the indoor air quality and increase contaminant accumulation by limiting the amount of fresh air that infiltrates the building. The goal of this study was to quantify how the contaminants from a faulty gas furnace in a household could impact the occupants. The gas furnace was located in an attached garage and leaked carbon monoxide (CO). Multizone and CFD simulations were caried out to determine if an air terminal device (ATD) with a changing geometry could improve the air quality. The goal of the ATD was to maintain a steady air throw in the garage, while the air flow in the ventilation system would change. A steady air throw should help to remove the carbon monoxide generated from the furnace and prevent infiltration into the household. The results show that with the use of the new ATD, it was possible to maintain a steady air throw and the infiltration of CO was lowered.

Migration characteristics of CO under forced ventilation after excavation roadway blasting: A case study in a plateau mine

Multiple toxic gases, such as carbon monoxide (CO), are generated after excavation roadway blasting of plateau mines. To eliminate environmental pollution in a timely manner and avoid potential occupational hazards to miners, a three-dimensional unsteady roadway model was established based on field data of the Pulang copper mine in Yunnan province, China. Computational Fluid Dynamics (CFD) method was used to explore the space-time evolution characteristics of CO under different working conditions, and the grey correlation analysis was applied to study the correlation values of the influencing factors on the CO dispersion coefficient in the roadway. The results demonstrate that in the early stage of the roadway with forced ventilation, the mass concentration of CO in the vortex area near the working area was obviously higher than elsewhere, and in the later stage of ventilation, the mass concentration of CO at the bottom of the roadway was higher than that at the top. The most significant changes of the CO appeared within 500 s before ventilation. The mass-weighted average concentration of CO in the cross-section of the roadway presented a Gaussian-like distribution with respect to the ventilation time. The first stage represented a period of rapid growth, and the second stage exhibited a period of variable speed decline. The ventilation time when the mass concentration of CO in the roadway reached the upper limit of occupational exposure was generally between 700 s and 900 s, and the safe re-entry time was greater than 15 min. The grey correlation analysis revealed that the major influencing factors of CO migration in the roadway of the plateau mine, were, in a descending sequence, as follows: the distance between ventiduct mouth and working face, ventilation volume, and altitude, and the corresponding correlation coefficients were 0.9931, 0.7792, and 0.4366, respectively. The altitude was inversely proportional to the CO dispersion coefficient, and the distance between ventiduct mouth and working face was directly proportional to the ventilation coefficient corresponding to the CO dispersion coefficient. This research can provide guidance on optimising the ventilation design of roadways in plateau mines, thus ensuring the occupational health of cleaners.

A quantitative approach to evaluate risks of spontaneous combustion in longwall gobs based on CO emissions at upper corner

Carbon monoxide (CO) is an important gas indicator for early detection and evaluation of spontaneous combustion in longwall gobs, and continuous monitoring of this gas is generally located at the upper corner of working face. Although CO emissions during spontaneous heating of coal have been investigated adequately in laboratory, few studies have involved in the migration and generation behavior of CO in longwall gobs. The CO-based early warning threshold for spontaneous combustion in gob is unsettled either. In this study, a fully coupled model of generation and transport of CO in longwall gob is developed by combining with air seepage, oxygen transport, thermal transfer, and exothermic reaction. Standard CO generation rate (SCOGR) as one key parameter is introduced for the better simulation on CO migration in gob. Our previously developed solving software of COMBASS-3D has been improved to investigate the functional relationship between progression of spontaneous combustion in longwall gob and CO emissions at upper corner. The results show that (i) the SCOGR depends strongly on temperature and coal properties, but is independent of ambient oxygen concentration, which is the basis for calculating actual CO generation rate; (ii) the high CO concentration zone overlaps with the oxidative self-heating zone and the high temperature zone in windward side of gob, which is consistent with the theoretical expectation and on-site observation; (iii) increasing longwall advance rate, decreasing ventilation flux and reducing thickness of abandoned coal all can not only reduce risks of spontaneous combustion in longwall gob but also suppress CO emissions from the gob; (iv) the maximum temperature in gob grows linearly with the increase of natural logarithm of CO concentration at upper corner in low temperature stage, and the early warning threshold can be calculated on basis of this relationship with the minimum self-heating temperatures of coal. These works can provide a quantitative approach for early warning the spontaneous combustion fires in longwall gobs.

Co and No Binding in Inducible Nitric Oxide Synthase

Nitric oxide synthases (NOSs) are homodimeric heme enzymes that catalyze the oxidative degradation of L-arginine (L-Arg) to nitric oxide (NO). Three structurally similar isoforms have been identified in endothelial cells (eNOS), neuronal tissues (nNOS) and in macrophages (iNOS). Different from eNOS and nNOS, iNOS is not present in resting cells but is expressed upon inflammatory and immunologic stimulation. As this isoform has been implicated in the pathogenesis of various diseases, there is a growing need for potent and highly selective inhibitors.The targeted development of potent inhibitors that are highly specific for iNOS requires detailed insights into the interaction between the ligand, the heme and the surrounding protein matrix on the molecular level. Therefore, we have investigated ligand and substrate binding in iNOSoxy using Fourier transform infrared (FTIR) spectroscopy in combination with temperature derivative spectroscopy (TDS). The physiological ligand O2 was replaced by carbon monoxide (CO) and NO. Both CO and NO allow us to exploit their excellent properties as spectroscopic probes. Previous studies on CO and NO migration in myoglobin have shown distinct differences in CO and NO migration despite their similar sizes.

Discrimination between CO and O2 in Heme Oxygenase: Comparison of Static Structures and Dynamic Conformation Changes following CO Photolysis

Heme oxygenase (HO) catalyzes heme degradation, one of its products being carbon monoxide (CO). It is well known that CO has a higher affinity for heme iron than does molecular oxygen (O(2)); therefore, CO is potentially toxic. Because O(2) is required for the HO reaction, HO must discriminate effectively between CO and O(2) and thus escape product inhibition. Previously, we demonstrated large conformational changes in the heme-HO-1 complex upon CO binding that arise from steric hindrance between CO bound to the heme iron and Gly-139. However, we have not yet identified those changes that are specific to CO binding and do not occur upon O(2) binding. Here we determine the crystal structure of the O(2)-bound form at 1.8 Å resolution and reveal the structural changes that are specific to CO binding. Moreover, difference Fourier maps comparing the structures before and after CO photolysis at <160 K clearly show structural changes such as movement of the distal F-helix upon CO photolysis. No such changes are observed upon O(2) photolysis, consistent with the structures of the ligand-free, O(2)-bound, and CO-bound forms. Protein motions even at cryogenic temperatures imply that the CO-bound heme-HO-1 complex is severely constrained (as in ligand binding to the T-state of hemoglobin), indicating that CO binding to the heme-HO-1 complex is specifically inhibited by steric hindrance. The difference Fourier maps also suggest new routes for CO migration.

Kinetics of Carbon Monoxide Migration and Binding in Solvated Neuroglobin As Revealed by Molecular Dynamics Simulations and Quantum Mechanical Calculations

Neuroglobin (Ngb) is a globular protein that reversibly binds small ligands at the six coordination position of the heme. With respect to other globins similar to myoglobin, Ngb displays some peculiarities as the topological reorganization of the internal cavities coupled to the sliding of the heme, or the binding of the endogenous distal histidine to the heme in the absence of an exogenous ligand. In this Article, by using multiple (independent) molecular dynamics trajectories (about 500 ns in total), the migration pathways of photolized carbon monoxide (CO) within solvated Ngb were analyzed, and a quantitative description of CO migration and corresponding kinetics was obtained. MD results, combined with quantum mechanical calculations on the CO-heme binding-unbinding reaction step in Ngb, allowed construction of a quantitative model representing the relevant steps of CO migration and rebinding.

Protein Collective Motions Coupled to Ligand Migration in Myoglobin

Ligand migration processes inside myoglobin and protein dynamics coupled to the migration were theoretically investigated with molecular dynamics simulations. Based on a linear response theory, we identified protein motions coupled to the transient migration of ligand, carbon monoxide (CO), through channels. The result indicates that the coupled protein motions involve collective motions extended over the entire protein correlated with local gating motions at the channels. Protein motions, coupled to opening of a channel from the distal pocket to a neighboring xenon site, were found to share the collective motion with experimentally observed protein motions coupled to a doming motion of the heme Fe atom upon photodissociation of the ligand. Analysis based on generalized Langevin dynamics elucidated slow and diffusive features of the protein response motions. Remarkably small transmission coefficients for rates of the CO migrations through myoglobin were found, suggesting that the CO migration dynamics are characterized as motions governed by the protein dynamics involving the collective motions, rather than as thermally activated transitions across energy barriers of well-structured channels.

Kinetics of Carbon Monoxide Migration and Binding in Solvated Myoglobin as Revealed by Molecular Dynamics Simulations and Quantum Mechanical Calculations

By using multiple (independent) molecular dynamics (MD) trajectories (about 500 ns in total) of photolized carbon monoxide (CO) within solvated myoglobin, a quantitative description of CO migration and corresponding kinetics is obtained. MD results combined with previously reported quantum mechanical calculations on the CO-heme binding-unbinding reaction step in myoglobin allowed construction of a detailed quantitative model, shedding light on the kinetic mechanism and relevant steps of CO migration and geminate binding. Finally, the obtained (unbiased) theoretical-computational model is critically compared with the available computational and experimental data for myoglobin in solution.

The Kinetics of Ligand Migration in Crystallized Myoglobin as Revealed by Molecular Dynamics Simulations

By using multiple molecular dynamics trajectories of photolyzed carbon monoxide (CO) within crystallized myoglobin, a quantitative description of CO diffusion and corresponding kinetics was obtained. Molecular dynamics results allowed us to construct a detailed kinetic model of the migration process, shedding light on the kinetic mechanism and relevant steps of CO migration and remarkably-well reproducing the available experimental data as provided by time-resolved Laue x-ray diffraction.

Monitoring and removal of CO in blasting operations

Toxic fumes produced by detonating explosives in surface mining and construction operations pose potential hazards to workers and the public. Blasting operations produce both toxic and nontoxic gaseous products; the toxic products are mainly carbon monoxide (CO) and the oxides of nitrogen (NO x ). Since 1988, there have been 17 documented incidents in the United States and Canada in which carbon monoxide (CO) is suspected to have migrated through ground strata into occupied enclosed spaces as a result of proximate trench blasting or surface mine blasting. These incidents resulted in 39 suspected or medically verified carbon monoxide poisonings as well as one fatality. At worst people may be fatally poisoned and the least to be expected is increased public objections to blasting. Local and state agencies could demand a cessation of the blasting requiring more expensive mechanical means to break the rock. This paper discusses the most feasible means of preventing CO migration, mitigating CO that has migrated, and detecting CO in an underground enclosed space and may help reduce the exposure of unsuspecting area residents to carbon monoxide and help prevent the implementation of unnecessary regulations and limitations on blasting. Single-hole shots and small-scale multiple-hole blasts were performed that indicate promising means of prevention and mitigation.

A Spectroscopic Study of Structural Heterogeneity and Carbon Monoxide Binding in Neuroglobin

Neuroglobin (Ngb) is a small globular protein that binds diatomic ligands like oxygen, carbon monoxide (CO) and nitric oxide at a heme prosthetic group. We have performed FTIR spectroscopy in the infrared stretching bands of CO and flash photolysis with monitoring in the electronic heme absorption bands to investigate structural heterogeneity at the active site of Ngb and its effects on CO binding and migration at cryogenic temperatures. Four CO stretching bands were identified; they correspond to discrete conformations that differ in structural details and CO binding properties. Based on a comparison of bound-state and photoproduct IR spectra of the wild-type protein, Ngb distal pocket mutants and myoglobin, we have provided structural interpretations of the conformations associated with the different CO bands. We have also studied ligand migration to the primary docking site, B. Rebinding from this site is governed by very low enthalpy barriers (∼1 kJ/mol), indicating an extremely reactive heme iron. Moreover, we have observed ligand migration to a secondary docking site, C, from which CO rebinding involves higher enthalpy barriers.

Photoinduced Carbon Monoxide Migration in a Synthetic Heme−Copper Complex

Time-resolved infrared (TRIR) flash photolytic techniques have been employed to initiate and observe the efficient dissociation of CO from a synthetic heme-CO/copper complex, [((6)L)Fe(II)(CO)..Cu(I)](+) (2), in CH(3)CN and acetone at room temperature. In CH(3)CN, a significant fraction of the photodissociated CO molecules transiently bind to copper (nu(CO)(Cu) = 2091 cm(-)(1)) giving [((6)L)Fe(II)..Cu(I)(CO)](+) (4), with an observed rate constant, k(1) = 1.5 x 10(5) s(-)(1). That is followed by a slower direct transfer of CO from the copper moiety back to the heme (nu(CO)(Fe) = 1975 cm(-)(1)) with k(2) = 1600 s(-)(1). Additional transient absorption (TA) UV-vis spectroscopic experiments have been performed monitoring the CO-transfer reaction by following the Soret band. Eyring analysis of the temperature-dependent data yields DeltaH(double dagger) = 43.9 kJ mol(-)(1) for the 4-to-2 transformation, similar to that for CO dissociation from [Cu(I)(tmpa)(CO)](+) in CH(3)CN (DeltaH(double dagger) = 43.6 kJ mol(-)(1)), suggesting CO dissociation from copper regulates the binding of small molecules to the heme within [((6)L)Fe(II)..Cu(I)](+)(3). Our observations are analagous to those observed for the heme(a3)/Cu(B) active site of cytochrome c oxidase, where photodissociated CO from the heme(a3) site immediately (ps) transfers to Cu(B) followed by millisecond transfer back to the heme.

Structural Dynamics Controls Nitric Oxide Affinity in Nitrophorin 4

Nitrophorin 4 (NP4) is one of seven nitric oxide (NO) transporting proteins in the blood-sucking insect Rhodnius prolixus. In its physiological function, NO binds to a ferric iron centered in a highly ruffled heme plane. Carbon monoxide (CO) also binds after reduction of the heme iron. Here we have used Fourier transform infrared spectroscopy at cryogenic temperatures to study CO and NO binding and migration in NP4, complemented by x-ray cryo-crystallography on xenon-containing NP4 crystals to identify cavities that may serve as ligand docking sites. Multiple infrared stretching bands of the heme-bound ligands indicate different active site conformations with varying degrees of hydrophobicity. Narrow infrared stretching bands are observed for photodissociated CO and NO; temperature-derivative spectroscopy shows that these bands are associated with ligand docking sites close to the extremely reactive heme iron. No rebinding from distinct secondary sites was detected, although two xenon binding cavities were observed in the x-ray structure. Photolysis studies at approximately 200 K show efficient NO photoproduct formation in the more hydrophilic, open NP4 conformation. This result suggests that ligand escape is facilitated in this conformation, and blockage of the active site by water hinders immediate reassociation of NO to the ferric iron. In the closed, low-pH conformation, ligand escape from the active site of NP4 is prevented by an extremely reactive heme iron and the absence of secondary ligand docking sites.

Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 2. Special working procedures to minimize CO migration

Carbon monoxide (CO) produced by blasting operations in civil engineering works in residential environments can migrate fair distances in the surrounding fractured bedrock and underground infrastructures in the blast area and can then infiltrate enclosed spaces. Poisoning of workers and people in general exposed to an emission of CO produced by explosives has occurred many times. Special working procedures must be developed to minimize the risk of poisoning. Three different procedures were tested in the field where the geologic conditions (slate confined with more than 0.5 m of clayey till) were favourable for CO migration. The first procedure tested aimed to minimize CO production and migration by changing the usual explosive type and the sequence of blasting, excavating and embanking the debris, and installing vents in the surrounding rock. This method did not have a significant effect on CO migration. The second method aimed to mitigate the CO produced by excavating the overburden before drilling, placing blast mats, excavating the broken rock after each blast, and changing the sequence of blasting. This procedure was efficient and safe. The third method consisted of pumping the interstitial air in the broken rock with a vacuum truck immediately after each blast. This method was a good alternative but requires monitoring of the exhaust air and was not as efficient and reliable as the excavation method.Key words: carbon monoxide, blasting, poisoning, enclosed spaces, remediation, house.

Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 1. CO production and migration mechanisms

Explosives used for blasting operations in civil engineering works can generate large volumes of carbon monoxide (CO). The production of 10–24 L of CO per kilogram of explosives blasted is theoretically possible. CO can migrate a considerable distance in the fractured rock of the blasted areas and then infiltrate closed spaces (sewage systems, manholes, basements of houses). In the Province of Quebec, in the last 10 years, seven people were poisoned by CO in their houses to the extent that they had to be treated in a hyperbaric chamber. Underground conduits broken by blasting, filling around underground conduits in road or house trenches, or fractured rock created by blasts between houses or between a house and a road are the different CO pathways identified in the Quebec incidents. Field tests done by our group show that (i) the structural geology of the rock formation (schistosity, family of joints and fractures) controls the direction and extent of gas migration in fractures generated by blasts; (ii) the confinement of the rock can affect the quantity of gas migrating in the fractured rock; (iii) significant concentrations of CO may persist in the fractured rock 7 days after a blast; (iv) advection is the initial mechanism of CO migration immediately after a blast, and the distance of migration varied from 8 m in the fractured rock to 20 m in the fills of a road trench; and (v) further CO migration by diffusion up to 15 m in the induced fractures and 30 m in fills may occur in the 3 days following a blast.Key words: carbon monoxide, blasting, poisoning, enclosed spaces, gas migration, house.

Laboratory studies of the interaction of carbon monoxide with water ice

The interaction of carbon monoxide (CO) with vapour-deposited water(H2O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption from amorphous H2Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as the water ice crystallises and then desorbs. The astronomical implications of this model are discussed.

Infrared Study of Carbon Monoxide Migration among Internal Cavities of Myoglobin Mutant L29W.

Myoglobin, a small globular heme protein that binds gaseous ligands such asO(2), CO and NO reversibly at the heme iron, provides an excellent modelsystem for studying structural and dynamic aspects of protein reactions. Flashphotolysis experiments, performed over wide ranges in time and temperature, reveal a complex ligand binding reaction with multiple kinetic intermediates, resulting from protein relaxation and movements of the ligand within the protein. Our recent studies of carbonmonoxy-myoglobin (MbCO) mutant L29W, using time-resolved infrared spectroscopy in combination with x-ray crystallography, have correlated kinetic intermediates with photoproduct structures that are characterized by the CO residing in different internal protein cavities, so-called xenon holes. Here we have used Fourier transform infrared temperature derivative spectroscopy (FTIR-TDS) to further examine the role of internal cavities in the dynamics. Different cavities can be accessed by the CO ligands at different temperatures, and characteristic infrared absorption spectra have been obtained for the different locations of the CO ligand within the protein, enabling us to monitor ligand migration through the protein as well as conformational changes of the protein.

Myoglobin Mutants Giving the Largest Geminate Yield in CO Rebinding in the Nanosecond Time Domain

We have measured the rebinding of carbon monoxide (CO) to some distal mutants of myoglobin (Mb) in the time range from 10 −8 to 10 −1 s by flash photolysis, in which the photodissociated CO rebinds to the heme iron without escaping to the solvent water from the protein matrix. We have found that the double mutants [His 64→Val/Val 68→Thr (H64V/V68T) and His 64→Val/Val 68→Ser (H64V/V68S)] have an extremely large geminate yield (70–80%) in water at 5°C, in contrast to the 7% of the geminate yield of wild-type Mb. The CO geminate yields for these two mutants are the largest in those of Mb mutants reported so far, showing that the two mutants have a unique heme environment that favors CO geminate rebinding. Comparing the crystal structures and 1H-NMR and vibrational spectral data of H64V/V68T and H64V/V68S with those of other mutants, we discuss factors that may control the nanosecond geminate CO rebinding and CO migration in the protein matrix.

CO migration on Pt(100) and Pt(11 1 1) surfaces studied by time resolved infrared reflection-absorption spectroscopy

Carbon monoxide (CO) migration on Pt(100) and Pt(11 1 1) single crystal electrode surfaces in an acid solution was studied by electrode potential modulated infrared reflection-absorption spectroscopy and time resolved infrared reflection-absorption spectroscopy. The interconversion of CO adsorbed on both electrode surfaces between on-top, asymmetric and symmetric bridge-bonded sites was caused by the applied electrode potentials. Unstable CO intermediate species were created during the interconversion of their sites.