Asphyxiants

Paraffins. Methane and ethane are simple asphyxiants, whereas the higher homologues are central nervous system depressants. Liquid paraffins can remove oil from exposed skin and cause dermatitis or pneumonia in lung tissue. Generally, paraffins are the least toxic class of hydrocarbons. 

Olefins, Diolefins, and Acetylenes. Members of this category having up to four carbon atoms are both asphyxiants and anesthetics, and potency for the latter effect increases with carbon chain length. Skin-contact effects are similar to those of paraffins. 

Simple asphyxiant value shown is 10% of the lower flammable limit (LFL). 

Propylene is a colorless gas under normal conditions, has anesthetic properties at high concentrations, and can cause asphyxiation. It does not irritate the eyes and its odor is characteristic of olefins. Propjiene is a flammable gas under normal atmospheric conditions. Vapor-cloud formation from Hquid or vapor leaks is the main ha2ard that can lead to explosion. The autoignition temperature is 731 K in air and 696 K in oxygen (80). Evaporation of Hquid propylene can cause skin bums. Propylene also reacts vigorously with oxidising materials. Under unusual conditions, eg, 96.8 MPa (995 atm) and 600 K, it explodes. It reacts violentiy with NO2, N2O4, and N2O (81). Explosions have been reported when Hquid propylene contacts water at 315—348 K (82). Table 8 shows the ratio TJTp where is the initial water temperature, and T is the superheat limit temperature of the hydrocarbon. 

Butylenes are not toxic. The effect of long-term exposure is not known, hence, they should be handled with care. Reference 96 Hsts air and water pollution factors and biological effects. They are volatile and asphyxiants. Care should be taken to avoid spills because they are extremely flammable. Physical handling requires adequate ventilation to prevent high concentrations of butylenes in the air. Explosive limits in air are 1.6 to 9.7% of butylenes. Their flash points range from —80 to —73° C. Their autoignition is around 324 to 465°C (Table 2). Water and carbon dioxide extinguishers can be used in case of fire. 

Products of Combustion Heat, hght, smoke, and asphyxiating and toxic gases are produced by fire. In a hot, well-ventilated fire, combustion is usually nearly complete. Nearly all the carbon is converted to carbon dioxide, all the hydrogen to steam, and oxides of various other elements such as sulfur and nitrogen are produced. 

Explosion prevention by inerting has several advantages over explosion protection techniques, such as explosion venting. For example, with successful inerting, fires or business interruptions cannot occur. Nevertheless, beware of the potential of asphyxiation with inerting proper vessel entry procedures must be implemented and occasionally it may be prudent to monitor for oxygen in workplaces. 

One has to be aware of the danger of asphyxiation from gases in inerted equipment. This is also important For surrounding areas in case of major leaks. 

When using inert gas, provide protection against personnel asphyxiation hazards... 

For filter boxes, provide remote and automatic filter box lid closing on trip of appropriate fire detection device. Fire detection device may also be interlocked to stop solvent feed, trip deluge internal to filter box and/or trip inert gas blanket for filter box (caution, be aware inert gas is a potential asphyxiation hazard)... 

Provide nitrogen backup to instrument air (caution be aware of potential asphyxiation hazards)... 

Unfortunately, even if everyone agrees on a tolerable risk value, there are many other subjective factors that influence our understanding (and tolerance) of risk. If 1 fatality per year were tolerable from causes such as falls, electrocutions, or asphyxiations, would TOO fatalities be... 

Equally, if your body requires more oxygen than the available oxygen in the atmosphere, then you would be asphyxiated. There must be more oxygen available in the air than the oxygen you consume. 

Hot gases rise by thermal lift. Henee in the open air they will disperse. Within buildings this is a serious eause of fire esealation and toxie/asphyxiation hazards if smoke and hot gases are able to spread without restrietion (or venting) to upper levels. 

Inerts Cases Simple asphyxiants Argon methane hydrogen nitrogen helium. Particulates e.g. cement, calcium carbonate. 

Skin proteetion may neeessitate use of full proteetive suits. When eatalysts are dumped from reaetors at the end of a proeess they may prove to be extremely dusty as a result of reduetion in partiele size during the reaetion proeess. Again, depending upon the nature of the hazard, ventilation, personal proteetion, and use of temporary enelosures to prevent contamination of the general work area should be considered. Some catalysts are pyrophoric and some catalyst beds are inerted with the added possibility of fire, or release of inerting gas into the workplace which may cause asphyxiation. 

Carbon dioxide gas ean aet as an asphyxiant due to displaeement of air, resulting in oxygen defieieney (page 262). Sourees inelude ... 

Simple asphyxiant. Some gases and vapours present at high concentrations act as asphyxiants by reducing the oxygen content of air. Many of these are odourless and colourless. Many also pose a fire or explosion risk, often at values below which asphyxiation can occur. (Although capable of asphyxiation, they are not considered to be substances hazardous to health under COSHH.)... 

Train staff in hazards and precautions, and practise emergency evacuation drills Remember that flammable chemicals can also be toxic or asphyxiant... 

Asphyxiation (except with oxygen) if the cryogen evaporates in a confined space. 

Even non-toxic gases are potentially hazardous owing to asphyxiation (oxygen deficiency). Irrespective of material, all equipment must be adequately designed to withstand process pressures. 

Aeetylene is a simple asphyxiant and anaestlietie. Pure aeetylene is a eolourless, highly flammable gas with an ethereal odour. Material of eommereial purity has an odour of garlie due to the presenee of impurities sueh as phosphine. Its physieal properties are shown in Table 9.4. Aeetylene, whieh eondenses to a white solid subliming at -83°C, is soluble in its own volume of water but highly soluble in aeetone. 

Propane has a eharaeteristie natural gas odour and is basieally insoluble in water. It is a simple asphyxiant but at high eoneentrations has an anaesthetie effeet. The TLV is 2500 ppm. It is usually shipped in low-pressure eylinders as liquefied gas under its own vapour pressure of ea 109 psig at 21°C. Its pressure/temperature profile is given in Figure 9.7. 

LPG is considered to be non-toxic witli no chronic effects, but the vapour is slightly anaesthetic. In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physical asphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g. methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell down to approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorant is not added for specific applications, e.g. cosmetic aerosol propellant. 

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