Exposures to carbon monoxide, hydrogen cyanide and their mixtures: interrelationship between gas exposure concentration, time to incapacitation, carboxyhemoglobin and blood cyanide in rats

Fast response and recovery polyaniline montmorillonite reduce graphene oxide polymer nanocomposite material for detection of hydrogen cyanide gas

In the present work, we have developed a polymer based gas sensor. The polymer nanocomposites are synthesized by the chemical oxidative polymerization of aniline with ammonium persulfate and sulfuric acid. The fabricated sensor is able to achieve a sensing response of 4.56% for PANI/MMT-rGO at 2 ppm of hydrogen cyanide (HCN) gas. The sensitivity of the sensors PANI/MMT and PANI/MMT-rGO are 0.89 ppm^-1 and 1.1174 ppm^-1 respectively. The increase in the sensitivity of the sensor may be due to an increase in the surface area provided by MMT and rGO which provided more binding sites for the HCN gas. The sensing response of the sensor increases as the concentration of the gas exposed increases but saturates after 10 ppm. The sensor recovers automatically. The sensor is stable and can work for 8 months.

Analysis of fire deaths in Poland and influence of smoke toxicity

Dwelling fires have changed over the years because building contents and the materials used in then have changed. They all contribute to an ever-growing diversity of chemical species found in fires, many of them highly toxic. These arise largely from the changing nature of materials in interior finishes and furniture, with an increasing content of synthetic materials containing higher levels of nitrogen, halogen and phosphorus additives. While there is still a belief that carbon monoxide is the major lethal toxic agent in fires, the hydrogen cyanide and acid gases released from these additives are now well-recognised as major contributory causes of incapacitation, morbidity and mortality in domestic fires. Data for the total number of 263 fire death cases in the Mazowieckie region (mainly Warsaw area) of Poland between 2003-2011 for dwellings fires were obtained from pathologists, forensic toxicologists, fire fighters and analysed. Factors contributing to the death such as the findings of the full post mortem examination (age, sex, health status, burns), the toxicological analysis (carbon monoxide, alcohol etc.), and a thorough investigation of the scene (fire conditions, fuel, etc.) were taken into account and are summarised.

Risk assessment in combustion toxicology: Should carbon dioxide be recognized as a modifier of toxicity or separate toxicological entity?

To characterize the accumulated hazards associated with the inhalation of gases typical of combustion products, a time-integrated value known as the fractional effective dose (FED) is used. This FED is maintained by the International Organization for Standardization (ISO) and made publicly available as the Standard ISO 13571. The current FED calculation related to asphyxiant gases is based on non-human primate data to estimate the 50% probability of humans to be incapacitated or not being able to execute any escape paradigm from fires. The objective of this paper was to compare two to calculate FEDs of the most common mixture of asphyxiant fire gases CO, HCN, and CO₂. The first was based on the current ISO 13571 (draft) standard, the alternative second method applied the conceptual principles established for the derivation of Acute Emergency Response Planning Guideline values. The alternative approach applied one third of the non-lethal threshold concentration (LC₀₁) as the most suitable and robust Point of Departure (POD) to estimate the threshold characterizing 'impairment of escape' in the absence of post-exposure mortality. The hyperventilation correction factor for CO₂ of ISO 13571 was replaced by a separate term that accounts for the inherent acute toxicity of CO₂. This analysis supports the conclusion that the current ISO 13571 standard misjudges the impact of the acute toxicity elicited by concentrations of CO₂ exceeding ≈6%. While underestimating the hazards attributable to CO₂, the hyperventilation adjustment factor suggested by this standard is biased to markedly overestimate the hazards assigned to CO and HCN in fire effluents.

Acute inhalation toxicity of carbon monoxide and hydrogen cyanide revisited: Comparison of models to disentangle the concentration × time conundrum of lethality and incapacitation

Contemporary emergency response planning guidelines are stratified to consider the threshold for serious toxicity and/or impairment of escape, relative to the potentially lethal level above this threshold and the lower level at which individuals should not experience or develop effects more serious than mild irritation. While harmonized testing guidelines and risk assessment paradigms are available for the quantification of thresholds for lethality or establishing no adverse effect levels, the quantification of 'impairment of escape' appears to be a more elusive goal. Approaches were explored in context with CO and HCN in past experimental combustion toxicology studies to estimate the time available for escape. This point of departure (POD) was compared with the non-lethal threshold (LC01) and one third thereof from published recent acute inhalation studies in rats examining the Cxt-matrix of both CO and HCN. The findings from this analysis suggest that the rat delivers the most consistent data. However, it remains challenging yet to bridge the behavioral variables of human behavior typical of escape to any surrogate animal model. For the asphyxiant gases examined, the PODs characterizing 'impairment of escape' were difficult to distinguish from those indicative of impending death. No specific modeled carboxyhemoglobin (COHb) level could be linked to onset of incapacitation. In summary, the higher ventilation of rats (kg body weight adjusted) renders this species even more susceptible than heavy breathing humans. LCt01 × 1/3 values derived from the comprehensive Cxt matrix of rat inhalation studies are considered to be most suitable and robust to estimate the human equivalent threshold (POD) of 'impairment of escape'.

Report on a study of fires with smoke gas development : determination of blood cyanide levels, clinical signs and laboratory values in victims

BACKGROUND

This is a report on an international non-interventional study of patients exposed to fires with smoke development in closed rooms. The objective of the study was to document clinical symptoms, relevant laboratory values and blood cyanide concentrations from fire victims in order to confirm or rule out presumptive correlations between the individual parameters.

MATERIALS AND METHODS

The study was conducted in five European countries with patients being included if they presented with the characteristic clinical signs, such as soot deposits and altered neurological status. Venous blood samples were taken from victims prior to administration of an antidote in all cases and determination of cyanide concentration was performed in a central laboratory using high performance liquid chromatography.

RESULTS

Data from 102 patients (62 % male, average age 49 years) were included in the evaluation with no blood samples being available for analysis from 2 patients. In 25 patients the blood cyanide concentration was below the limit of detection of 1.2 μmol/l. Cyanide levels between 1.2 and 10 μmol/l were measured in 54 patients, 7 patients had values between 10 and 20 μmol/l, 4 patients between 20 and 40 μmol/l while levels above 40 μmol/l were determined in 10 patients. The results of the study could not demonstrate that the cyanide level was influenced either by the interval between smoke exposure and blood sampling or the duration presence at the fire scene. The following clinical signs or laboratory values were recorded as relevant for increased and possibly toxic cyanide levels: respiratory arrest, dyspnea, resuscitation requirement, tracheal intubation, respiratory support measures, low Glasgow coma scale (GCS) score and respiratory frequency. A correlation between cyanide concentration and the total amount of soot deposits on the face and neck, in the oral cavity and in expectoration was confirmed. A correlation between cyanide and carboxyhemoglobin (COHb) levels in the blood of fire victims was also confirmed.

CONCLUSIONS

As long as it is not possible to immediately determine the blood cyanide concentration in patients exposed to fire with smoke development, a decreased GCS score, soot deposits particularly in expectoration, dyspnea and convulsions are to be regarded as risk markers for intoxication. In their presence immediate administration of hydroxocobalamin as an antidote is recommended.

Nitrite-mediated antagonism of cyanide inhibition of cytochrome c oxidase in dopamine neurons

Cyanide inhibits aerobic metabolism by binding to the binuclear heme center of cytochrome c oxidase (CcOX). Amyl nitrite and sodium nitrite (NaNO(2)) antagonize cyanide toxicity in part by oxidizing hemoglobin to methemoglobin (mHb), which then scavenges cyanide. mHb generation is thought to be a primary mechanism by which the NO(2)(-) ion antagonizes cyanide. On the other hand, NO(2)(-) can undergo biotransformation to generate nitric oxide (NO), which may then directly antagonize cyanide inhibition of CcOX. In this study, nitrite-mediated antagonism of cyanide inhibition of oxidative phosphorylation was examined in rat dopaminergic N27 cells. NaNO(2) produced a time- and concentration-dependent increase in whole-cell and mitochondrial levels of NO. The NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxy 3-oxide (PTIO) reversed this increase in cellular and mitochondrial NO. NO generated from NaNO(2) decreased cellular oxygen consumption and inhibited CcOX activity. PTIO reversed the NO-mediated inhibition, thus providing strong evidence that NO mediates the action of NaNO(2). Under similar conditions, KCN (20muM) inhibited cellular state-3 oxygen consumption and CcOX activity. Pretreatment with NaNO(2) reversed KCN-mediated inhibition of both oxygen consumption and CcOX activity. The NaNO(2) antagonism of cyanide was blocked by pretreatment with the NO scavenger PTIO. It was concluded that NaNO(2) antagonizes cyanide inhibition of CcOX by generating of NO, which then interacts directly with the binding of KCN x CcOX to reverse the toxicity. In vivo antagonism of cyanide by NO(2)(-) appears to be due to both generation of mHb and direct displacement of cyanide from CcOX by NO.

Efficacy of hydroxocobalamin for the treatment of acute cyanide poisoning in adult beagle dogs

INTRODUCTION

The efficacy of hydroxocobalamin for acute cyanide poisoning was compared with that of saline vehicle in dogs.

METHODS

Anesthetized adult beagle dogs were administered potassium cyanide (0.4 mg/kg/min, IV) until 3 min after the onset of apnea. Hydroxocobalamin (75 mg/kg [n = 19] or 150 mg/kg [n = 18], IV) or saline vehicle [n = 17] was then infused over 7.5 min while animals were ventilated with 100% oxygen, which was stopped after 15 min.

RESULTS

In vehicle-treated animals cyanide produced deterioration that culminated in a moribund state requiring euthanasia within 4 h in 10 of 17 animals and in neurological deficits necessitating euthanasia within 2-4 d in an additional 4 animals (mortality rate 82%). Survival through 14 d was observed in 15 of 19 animals administered hydroxocobalamin 75 mg/kg (mortality rate 21%), and 18 of 18 administered hydroxocobalamin 150 mg/kg (mortality rate 0%).

CONCLUSION

Hydroxocobalamin reversed cyanide toxicity and reduced mortality in a canine model.

Consequences of brief exposure to high concentrations of carbon monoxide in conscious rats

Exposure to high-concentration carbon monoxide (CO) is of concern in military operations. Experimentally, the physiologic manifestations of a brief exposure to elevated levels of CO have not been fully described. This study investigated the development of acute CO poisoning in conscious male Sprague-Dawley rats (220-380 g). Animals were randomly grouped (n = 6) and exposed to either air or 1 of 6 CO concentrations (1000, 3000, 6000, 10,000, 12,000, or 24,000 ppm) in a continuous air/CO dynamic exposure chamber for 5 min. Respiration was recorded prior to and during exposures. Mixed blood carboxyhemoglobin (COHb) and pH were measured before and immediately after exposure. Before exposure the mean baselines of respiratory minute volumes (RMVs) were 312.6 +/- 43.9, 275.2 +/- 40.8, and 302.3 +/- 39.1 ml/min for the 10,000, 12,000 and 24,000 ppm groups, respectively. In the last minute of exposure RMVs were 118.9 +/- 23.7, 62.1 +/- 10.4, and 22.0 +/- 15.1% (p < .05) of their mean baselines in these 3 groups, respectively. Immediately after exposure, blood COHb saturations were elevated to 60.16, 63.42, and 69.37%, and blood pH levels were reduced to 7.43 +/- 0.09, 7.25 +/- 0.05, and 7.13 +/- 0.04 in the 3 groups, respectively. Mortality during exposure was 1/12 in the 12,000 ppm group and 4/12 in the 24,000 ppm group. Deaths occurred close to the end of 5 min exposure. In each animal that died by exposure, pH was <6.87 and COHb saturation was >82%. Blood pH was unaltered and no death occurred in rats exposed to CO at concentrations <6000 ppm, although COHb saturations were elevated to 14.52, 29.94, and 57.24% in the 1000, 3000, and 6000 ppm groups, respectively. These results suggest that brief exposure to CO at concentrations <10,000 ppm may produce some significant physiological changes. However, exposure to CO at concentrations >10,000 ppm for brief periods as short as 5 min may change RMV, resulting in acute respiratory failure, acidemia, and even death.

Carbon Monoxide and Cyanide Poisoning in Fire Related Deaths in Victoria, Australia

OBJECTIVE

This study was undertaken to examine the association of hydrogen cyanide and carboxyhaemoglobin in victims of fire related deaths in Australia. The secondary aim was to document demographic data about Australian fire related deaths.

METHODS

An observational retrospective study was undertaken of autopsy reports from the Victorian Institute of Forensic Medicine. Reports of fire related deaths were electronically searched using the terms burns, "smoke" or "fire" as a cause of death in the calender years 1992 to 1998. Data on the circumstances of the fire and results of toxicological screening were obtained on 178 persons. Additional whole blood cyanide levels were determined if blood samples were available in storage. Demographics of the victims were analysed, as well as the relationship between carboxyhaemoglobin and whole blood cyanide levels.

RESULTS

Most (82%) of the victims died at the scene, whilst 32 victims died after a period of hospitalisation (hours to weeks). Suicide as a result of self-immolation was the reported cause of death in 32 cases. Most of the fires were in houses (114) and cars (29). The blood ethanol level was zero in 112 cases; the remaining cases (53) had a mean level of 0.17%. Other central nervous system (CNS) depressants were recorded in 49 of the 134 cases that received a complete toxicological screen. Carboxyhaemoglobin levels were measured in only 154 of 178 cases. The carboxyhaemoglobin level was zero in 43 cases. The remaining cases (111) had a mean level of 40%; with 44 cases having a level greater than 50%, a level considered to be potentially lethal. Whole blood hydrogen cyanide levels were measured in only 138 of 178 cases. The hydrogen cyanide level was zero in 52 cases. The remaining cases (86) had a mean level of 1.65 mg/L; with 11 cases having a level greater than 3.0 mg/L (potentially fatal). Blood ethanol levels were significantly correlated with both carboxyhaemoglobin (R = 0.22, P < 0.01) and cyanide (R = 0.36, P < 0.001). In addition, a significant correlation (r = 0.34) between carboxyhaemoglobin and hydrogen cyanide levels was noted.

CONCLUSIONS

This study showed a correlation between elevated blood ethanol and whole blood cyanide levels (r = 0.36, p < 0.001) and between elevated carboxyhaemoglobin and hydrogen cyanide levels (r = 0.34). Although the mean cyanide level was 1.3 mg/L (above the level some consider potentially toxic) in those cases with a carboxyhaemoglobin level of greater than 10%, there is insufficient data to permit recommendations for clinical care. Further studies are required on those victims that reach hospital alive.

Toxicity of fire smoke

This review is an attempt to present and describe the major immediate toxic threats in fire situations. These are carbon monoxide, a multitude of irritating organic chemicals in the smoke, oxygen depletion, and heat. During the past 50 years, synthetic polymers have been introduced in buildings in very large quantities. Many contain nitrogen or halogens, resulting in the release of hydrogen cyanide and inorganic acids in fire smoke as additional toxic threats. An analysis of toxicological findings in fire and nonfire deaths and the results of animal exposures to smoke from a variety of burning materials indicate that carbon monoxide is still likely to be the major toxicant in modern fires. However, the additional toxic threats mentioned above can sometimes be the principal cause of death or their addition can result in much lower than expected carboxyhemoglobin levels in fire victims. This analysis also revealed that hydrogen cyanide is likely to be present in appreciable amounts in the blood of fire victims in modern fires. The mechanisms of action of acute carbon monoxide and hydrogen cyanide poisonings are reviewed, with cases presented to illustrate how each chemical can be a major contributor or how they may interact. Also, lethal levels of carboxyhemoglobin and cyanide in blood are suggested from an analysis of the results of a large number of fire victims from different fire scenarios. The contribution of oxygen depletion and heat stress are more difficult to establish. From the analysis of several fire scenarios, they may play a major role in the room of origin at the beginning of a fire. The results in animal studies indicate that when major oxygen depletion (<10%) is added to lethal or sublethal levels of carbon monoxide or hydrogen cyanide its major role is to substantially reduce the time to death. In these experiments the carboxyhemoglobin level at death was slightly reduced from the expected level with exposure to carbon monoxide alone. However, blood cyanide was reduced by a factor of ten from the expected level with exposure to hydrogen cyanide alone. This is another factor (among many other presented) complicating the task of establishing the contribution of cyanide in the death of fire victims, from its analysis in their blood. Finally the role of ethanol intoxication, as it may influence carboxyhemoglobin levels at death, is reviewed. Its role is minor, if any, but the data available on ethanol in brain tissue and blood of fire victims confirmed that brain ethanol level is an excellent predictor of blood ethanol.

A fatality caused by accidental production of hydrogen sulfide

A 55-year-old male Caucasian truck driver was dead at the scene after breathing hydrogen sulfide (H(2)S) produced by an accidental transfer of sodium hydrogen sulfide (NaHS) from a tanker truck to a tank containing 4% sulfuric acid (H(2)SO(4)) and iron(II) sulfate (FeSO(4)). Autopsy of the decedent's body revealed pulmonary edema and passive congestion in lungs, spleen, kidneys, and adrenal glands. Postmortem biological samples were analyzed for carbon monoxide, cyanide, ethanol, and drugs. Since a potential exposure to H(2)S was involved, blood was also analyzed for sulfide (S(2-)). The analysis entailed isolating S(2-) from blood as H(2)S using 0.5M H(3)PO(4), trapping the gas in 0.1M NaOH, and determining the electromotive force using a sulfide ion specific electrode. Acetaminophen at a concentration of 14.3 microg/ml was found in blood, and metoprolol was detected in the blood, liver, and kidney samples. The blood S(2-) level was determined to be 1.68 microg/ml. It is concluded that the cause of death was H(2)S poisoning associated with a hazardous material accident in an industrial situation.

Blood carbon monoxide and hydrogen cyanide concentrations in the fatalities of fire and non-fire associated civil aviation accidents, 1991-1998

Blood samples submitted to the Civil Aeromedical Institute (CAMI) from aviation accident fatalities are analyzed for carbon monoxide (CO), as carboxyhemoglobin (COHb), and hydrogen cyanide, as cyanide (CN(-)). These analyses are performed to establish possible exposure of victims to smoke from in-flight/post-crash fires or to CO from faulty exhaust/heating systems. The presence of both gases in blood would suggest that the victim was alive and inhaled smoke. If only COHb is elevated, the accident (or a death) could be the result of CO contamination of the interior. Information pertaining to blood levels of these gases in aviation fatalities, in relation to the associated accidents, is scattered or not available, particularly with regard to toxicity. Therefore, considering that COHb> or =10% and CN(-)> or =0.25 microg/ml are sufficient to produce some degree of toxicological effects, the necessary information was extracted from the CAMI database. Samples from 3857 fatalities of 2837 aviation accidents, occurring during 1991-1998, were received; 1012 accidents, encompassing 1571 (41%) fatalities, were fire associated, whereas 1820 accidents were non-fire related. The remaining five accidents were of unknown fire status. There were fewer fire related fatalities and associated accidents in the (COHb> or =10% and CN(-)> or =0.25 microg/ml) category than that in the (COHb<10% and CN(-)<0.25 microg/ml) category. No in-flight fire was documented in the former category, but in-flight fires were reported in 14 accidents (18 fatalities) in the latter category. No non-fire accident fatality was found wherein levels of both gases were determined to be at or above the stated levels. There were 15 non-fire accidents with 17 fatalities wherein only COHb (10-69%) was elevated. The present study suggests that aviation fire accidents/fatalities were fewer than aviation non-fire accidents/fatalities and confirms that aviation accidents related to in-flight fires and CO-contaminated interiors are rare.