Basic Knowledge On Gases

Combustible Gas

  Combustible gases are any type of gas that can potentially ignite when mixed with oxygen or an oxidizing agent. In the context of occupational safety and the use of hazardous materials (HAZMAT), an oxidizing agent is a material that can cause or enhance the combustion of another material, usually by yielding oxygen.

  Combustible gases are typically made of hydrocarbons, carbon monoxide, hydrogen, or a combination of them. Butane, propane, ethane, and methane are common hydrocarbon-based combustible gases used in a variety of occupational settings.

  The dangers associated with combustible gas are severe. Unwanted or uncontrolled combustion can lead to fatal harm as a result of burns due to fire or injury due to explosion.

  In addition to the immediate danger posed by a combusting gas, the potential for the combustion to ignite other flammable materials, damage safety equipment, or create hazardous flying debris all pose significant secondary risks. As such, the physical properties of a gas do not entirely define how hazardous it is – the nature of the environment that the gas is being used in, and the hazards associated with that environment, are also relevant factors.

  Due to their common use in a variety of industrial settings, combustible gasses pose a danger to a variety of occupations. These include petrochemical industries, mining, and other types of enclosed space work, as well as many warehouse settings in which fuel is present. Certain settings that store significant amounts of pure oxygen, such as hospitals, may also have combustible gas concerns, as high volumes of pure oxygen can create combustion hazards in otherwise safe environments.

Combustible Gas Regulations

  Employers operating facilities that use combustible gas are subject to numerous regulatory requirements. Many of these regulations are directly concerned with ensuring that the gases are safely stored, handled, and transported. However, other combustible gas regulations are chiefly concerned with avoiding ignition sources. For example, OSHA standard 1910.307 – Hazardous (Classified) Locations is concerned with ensuring that electrical equipment does not pose an ignition hazard in areas with combustible gases or other combustible materials.

  Transportation regulators also play a large role in governing how hazardous materials are used and handled, and this includes combustible gases and oxidizers. Industry-specific agencies, such as the Mine Safety and Health Administration, may provide additional obligations and requirements in their specific areas of interest.

Assessing Combustible Gas Hazards

  The dangers that are directly associated with a given combustible gas can be understood by assessing a number of its physical properties.

Flash Point

  The flash point is the lowest temperature at which a specific non-gaseous solid or liquid substance will give off sufficient amounts of vapor to create a combustion hazard at the surface of the substance. A vapor is the gaseous form of a substance emitted by a volatile liquid or solid, such as gasoline.

Explosive Range

  The explosive range of a combustible gas is the range of concentrations (measured as a percentage of volume in air) at which a gas will ignite or explode when exposed to an ignition source. The explosive range is defined by two boundaries: the lower explosive/flammability limit (LEL/LFL) and the upper explosive/flammability limit (UEL/UFL).

  If the concentration of a combustible gas in the air is below the LEL, then the air is considered too "lean" to burn. If the concentration is above the UEL, there will not be enough oxygen to sustain the combustion. In order to understand the level of hazard associated with a given occupational setting, it is vital to know the LEL and UEL of a gas and to be able to monitor the air in order to ensure that the concentration remains outside of the explosive range.

  In the United States, OSHA's combustible gas regulations rely heavily on the explosive range to define workplace safety obligations. For instance, standard 1910.146 – Permit Confined Spaces classifies any confined space in which a combustible gas is present at a concentration of at least 10% of its LEL as being a hazardous atmosphere.

Vapor Density

  Vapor density is the relative weight of a vapor in comparison to ordinary air. If a vapor is heavier than air, it may "spill" into low-lying areas and accumulate over time. This is why explosive gases can be a significant hazard in mines, sewers, and other underground spaces.

Auto-Ignition Temperature

  Auto-ignition temperature is the temperature at which a combustible gas will ignite without exposure to an outside ignition source. This is sometimes referred to as the spontaneous ignition temperature (SIT), and is of chief concern in high-heat environments.

Carbon Monoxide

  Carbon monoxide is a gas that is less dense then air. It has no color, no taste and no smell. It is a toxic gas when inhaled in higher concentrations. It is found in the fumes that are produced when burning fuels used in vehicles, small engines, stoves, gas ranges and furnaces. Toxic carbon monoxide levels can build up in indoor areas that are not well ventilated, proving deadly to those who breathe it in.Carbon monoxide has triple bonds in which oxygen is connected with a carbon atom. Out of the three bonds two are covalent bonds. Carbon monoxide is produced by partial burning of carbon containing compounds. In biological activities carbon monoxide is produced by the breakdown of hemoglobin. It is used in the chemical industry for the production of aldehydes.

  It is also used in the meat industry for meat coloring to make the meat look fresh. In the medicine industry carbon monooxide is used as anti-inflammatory.

  When zinc Zn reacts with calcium carbonate CaCO3, it forms Zinc oxide ZnO and calcium oxide CaO plus Carbon monoxide CO. The reaction can be shown as follows:

Zn + CaCO3 – ZnO + CaO + CO

Volatile Organic

  Volatile organic compounds (VOC's) are a group of carbon based chemicals that evaporate at room temperature. While many VOC's can be readily smelled, some of them have no odour. The strength of the odour does not indicate the level of toxicity. Thousands of common VOC's are used in daily living.

  The level of volatile organic compounds is two to three times higher indoors than it is outdoors. The indoor concentration depends on such factors as the amount of VOCs in the product, the rate of VOC release, the volume of the air, the available ventilation and the outdoor concentration of VOCs.

  Breathing low levels of VOCs over a long period of time may increase the risk of health problems for some individuals.

Carbon Dioxide

  Carbon dioxide (CO2) is a colorless, odorless, incombustible gas. It is heavier than the air and soluble in water. It is normally found in the form of gas and found in the atmosphere (about 0.04%), but can also be found in liquid or solid state when suitably pressurized. Excessive carbon dioxide is injurious to human and animal health. Humans breathing air with more than a 5 percent concentration of carbon dioxide will lose consciousness in minutes and eventually die.

  Carbon dioxide is used in fire extinguishers, carbonated beverages, food refrigeration, for inflating life rafts and life jackets, blasting coal, foaming rubber and plastics, and as a food additive. Carbon dioxide is often compressed, and canisters can explode if exposed to heat (above 125.6 F). Contact with compressed CO2 can also cause frostbite. Exposure to airborne CO2 can cause asphyxiation and death.