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ASCE has developed a code of ethics for Civil Engineers. The code includes seven canons. The first canon states:.
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ASCE has developed a code of ethics for Civil Engineers. The code includes seven canons. The first canon states: CANON 1.Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties. ASCE then defined sustainable development to mean: Sustainable development is the challenge of meeting human needs for natural resources, industrial products, energy, food, transportation, shelter and effective waste management while conserving and protecting environmental quality and the natural resource base essential for future development.
One of the earliest and most popular definitions of sustainable development has come from The World Commission on Environment and Development (1987): Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Natural resources fall into one of two categories, renewable or non-renewable. Renewable resources include things like , fish, forests, solar energy, tidal influences, waves, hydro power, and wind power. Non-renewable resources include natural resources which have finite quantities such as coal, natural gas, and oil. Obviously, he use of renewable resources is most desirable.
The US EPA defines green engineering as: The design, commercialization, and use of processes and products, which are feasible and economical while minimizing generation of pollution at the source and risk to human health and the environment. The nine principles of green engineering are:
The key to green engineering is to apply these principles when they are most economical and feasible, in the early stages of design and development. Risk assessment tools can be used to select appropriate sustainable solutions. Risk of processes can be characterized by determining the exposure and toxicity of various processes. Then risk may be managed by the selection of the appropriate process.
The relationship between sustainable development, green engineering, and sustainability is shown in the figure below. Figure 7.1 Relationship between sustainable development, green engineering, and sustainability.
Materials Selection One of the decisions made by an engineer during the design process is typically the selection of the best material for the project. Traditionally the engineer selects the best material based on such factors as strength, stiffness, density, resistant to corrosion, cost and other material properties. Green engineering and sustainability principles would also suggest that the severity of the impact on the environment should be included in this selection process. Doing this accurately is very complex and a generally accepted methodology has not been devised, however.
For example, one approach which has been used is to compare the amount of energy used to produce the product from various types of materials. The material requiring the least amount of energy would be selected, since it would presumably have the least impact on the environment. Consider for example a product that may be made from carbon steel. Compare the amount of energy required to make the steel as shown in the figure below. If the same product were made form aluminum the energy cost to the aluminum would be much higher. This probably oversimplifies the problem. What if the product were made form recycled aluminum? Recycled aluminum requires only about 12% of the energy that newly formed aluminum requires. For some products it is not the energy required to produce the product that is important, but the energy required for the products use. Consider cars or vacuum cleaners for example. In actuality what should be considered is what we would call a life cycle cost, the total energy required for production, manufacture, use, and disposal or recycling.
When materials are selected more than just the energy condiserations need to be made. What about other air emissions, toxicity, resource depletion, potential for recycling, disposal costs? To further complicate the problem, recognize that it is necessary to quantify how each of these factors impacts human health, damages the ecosystem, and depletes resources. Then we have to realize that the importance of each of these factors are considered to be different by different people and groups. To help simplify the process an attempt has been made to determine a single indicator of a materials desirability. This method assigns a single measure or indicator to each material called an “eco-indicator” that reflects the perceived extent of the materials environmental impact. A search for “eco-indicators” on the internet will give you a lot ore information about this subject. A nice idea, but the accuracy is questionable and their use is still controversial.
Nuclear Physics Atomic number represents the number of protons in the nucleus Nucleus also contains nuetrons The mass number of an atom is the sum of the protons and neutrons Elements with the same atomic number but different mass numbers are called isotopes. One way of distinguishing isotopes is to write the chemical symbol with the mass number written as a superscript to the left to the symbol and the atomic number as a subscript also to the left of the symbol:
Some atoms are naturally unstable. Those elements that have more than 83 protons are considered naturally radioactive. Radioactive elements emit various forms of radiation as they decay to more stable forms. The three major forms of radiation are alpha particles, beta particles, and gamma rays. An alpha particle is essentially a helium nucleus, two protons and two neutrons. Alpha particles are relatively speaking large , slow moving and easily stopped. Because they cannot penetrate tissue very far the alpha particle tends to be only harmful when it is ingested. When an alpha particle is emitted from an atom its atomic number decrease by 2 and the mass number decreases by four. For example:
A beta particle is a free electron emitted from an unstable nucleus during the spontaneous transformation of a neutron into a proton and an electron. When this happens the atomic number of an atom increases by one and the mass number stays the same. Consider: Beta particles are negatively charged and travel further and penetrate deeper than alpha particles. Concrete, steel lead and water may be used to protect people from exposure to beta particles. Gamma radiation or gamma rays are electrmagnetic waves or photons that do not have mass or charge and travel at the speed of light. This is a damaging type of radiation because it is highly penetrating. Several centimeters or several feet of lead, concrete or lead-glass must be used to shield individuals from gamma radiation.
Einstein’s energy-mass-equivalency equation is used to calculate the energy associated with the release of energy from radionuclides: E = mc2 Where: E = energy g . Cm/s (ergs) m= mass of the particle, g c = speed of light (2.998 X 1010 cm/s) When radioactive decay occurs there is a loss of mass from the system. The energy produced is present in kinetic energy of any alph or beta particles emitted plus the energy of the gamma radiation. These particles are slowed and the gamma rays are absorbed as the radiation travels through matter and the energy is converted into thermal energy.
Many naturally occurring radioactive atoms are found on the earth. Primordial radionuclides: Uranium and Thorium are the best known. They have no stable isotope and eventually decay to lead isotopes. Potassium-40 is another that decays to its stable form of nonradioactive potassium Cosmogenic radionuclides: formed by the cosmic-ray bombardment of the earths atmosphere. There are 22 different cosmogenic radionuclides that eventually become part of plants and animals. The best known are carbon-14, hydrogen-3, and berylium-7
Units of Radioactivity The basic unit is the curie (Ci). One Ci corresponds to approximately 3.7 x 1010 disintegrations per second, the rate of decay of one gram of Radium. We are constantly naturally exposed to radiation through the air we breathe and the food we eat. The unit used to measure radioactive exposure is called the picoCurie. A picoCuire (pCi) is one-trillionth of a curie and equal to about 2.22 disintegrations per minute. A typical adult contains the following: 30 pCi Uranium, 3 pCi Thorium, 30 pCi of Radium, 110,000 pCi K-40, and 400,000 pCi C-14. The energy released from as these radionuclides decay can be measured and is called the dose. The internal dose is the maount of radioactivity deposited in our bodies from the radionuclides we ingest or inhale. The external dose comes mostly from gamma rays emitted by terrestrial sources like the ground and buildings along with cosmic rays.
The unit of gamma or x-ray radiation intensity is called the roentgen (R). 1 R is defined as the amount of gamma or X-ray radiation that will produce one electrostatic unit of electricity in one cubic centimeter of dry air at 0oC and 760 mm of pressure. This represents the exposure in air and must be translated to an absorbed dose. The term radiation absorbed dose (rad) corresponds to the absorption of 100 ergs of energy per gram and can be used for any type of radiation. In Si units the unit of absorbed dose is the gray (Gy). One Gy is equal to the absorption of 1 joule of energy per Kg of substance. One Gy is100 rads. The effect that different types of radiation has on humans is measured in roentgen equivalent man (rem). The Si equlivalent, sievert (Sv) is a unit of biological dose equal to the radiation dose having the same biological effect as one Gy or gamma radiation. One seivert is equal to 100 rem. In the US the standard absorbed dose in the rem and the annual dose is 300 millirem (mrem). Example use Adult workers at a nuclear plant are restricted to 5 rem per year, minors to 0.5 rem
Nuclear Fission and Nuclear Reactors In a nuclear reactor, neutrons bombard uranium or lputonium atoms causing splitting (fission) of their nucleus. Two fission fragments, gamma rays, and two or three neutrons are produced for each atom that is fissioned. Nuclear reactors get their energy primarily from the conversion of the kinetic energy fo the fission fragments into thermal energy. This energy is used to heat water, produce steam, and drive a turbine to produce electricity. Except for the heat source the process is just the same as fossil fueled plants. About 5.3 X 106 kWh of energy is released from the fission of one gram atom of uranium-233, uranium-235, or plutonium-239 or about 4.1 X 109 kcal per kg. By comparison burning one Kg coal or one Kg gasoline releases 6939 and 12,000 kcal/kg respectively.
The problem is that the fission fragments and they along with other radioactive waste components such as Pu-239 represent very significant handling, transport, and disposal problems. Radioactive decay may be modeled as a first order reaction: From this equation:
Waste disposal Breeder Reactors Immobilization and underground disposal
Case Histories New Chairs from Haworth and Steelcase Paper or Plastic Selection of Materials for Beverage Containers Coal vs. Nuclear Energy
Figure 7.2 Schematic of type 2 advanced integrated waste-water pond system.
