Acoustic hazards

Acoustic hazards low and high frequency noise, ultrasound, explosive waves, thunder. 

Moderate (attenuation and limitation of effects) Use vacuum to reduce boiling point Reduce process temperatures and pressures Refrigerate storage vessels Dissolve hazardous material in safe solvent Operate at conditions where reactor runaway is not possible Place control rooms away from operations Separate pump rooms from other rooms Acoustically insulate noisy lines and equipment Barricade control rooms and tanks... 

An in vitro investigation into the bactericidal effects of a dental ultrasonic descaler on bacterial biofilms using Actinobacillus actinomycctcmcomitans and Porphyromonas gin-givalis has been reported [49]. Suspensions of the bacteria were subjected to the vibrations of a Cavitron PI insert for 2.5 and 5.0 min in an acoustically-simulated model substrate. A 60 % kill rate was achieved at a temperature of around 50 °C which constituted an alternative treatment for bacterial biofilms. This study suggested that a similar approach could be used in the clean-up of a range of biofQms considered to be the cause of a range of environmental hazards. 

A very important point occurs in the transmission of acoustic power into a liquid which is termed the cavitation threshold. When very low power ultrasound is passed through a liquid and the power is gradually increased, a point is reached at which the intensity of sonication is sufficient to cause cavitation in the fluid. It is only at powers above the cavitation threshold that the majority of sonochemical effects occur because only then can the great energies associated with cavitational collapse be released into the fluid. In the medical profession, where the use of ultrasonic scanning techniques is widespread, keeping scanning intensities below the cavitation threshold is of vital importance. As soon as the irradiation power used in the medical scan rises above this critical value, cavitation is induced and, as a consequence, unwanted even possibly hazardous chemical reactions may occur in the body. Thus, for both chemical and medical reasons there is a considerable drive towards the determination of the exact point at which cavitation occurs in liquid media, particularly in aqueous systems. Historically, therefore, the determination of the cavitation threshold was one of the major drives in dosimetry. 

Headliners are particularly complex textile-based composites because not only do they incorporate acoustic insulative materials but they also incorporate components such as internal mirrors, interior lighting, and associated wiring - a particular fire hazard. A typical structure described by Fung and Hardcastle shows that up to seven or more component layers may be present in a modem headliner, as outlined in Table 11.11 such a structure is truly a technical textile. The whole composite must be thermoformable with individual layers bound together using adhesive films or powders. Careful selection of each component is essential if it is to pass FMVSS 302 without the need for additional flame retardant treatment. 

S.L. Rose-Pehrsson, J.W. Grate, D.S. BaUantine, P.C. Jurs, Detection of hazardous vapors including mixtures using pattern recognition analysis of responses from siuface acoustic wave devices. Anal. Chem. 60, 2801-2811 (1988)... 

Schwan was one of the founders of biomedical engineering as a new discipline. Before World War II, in the laboratory of Rajewski at the Frankfurter Institut fiir Biophysik, he had started with some of the most important topics of the field on low-frequency blood and blood serum conductivity, counting of blood cells, selective heating and body tissue properties in the ultra-high-frequency range, electromagnetic hazards and safety standards for microwaves, tissue relaxation, and electrode polarization. He also worked with the acoustic and ultrasonic properties of tissue. In 1950, he revealed for the first time the frequency dependence of muscle... 

Ultrasound through airborne conduction does not appear to pose a significant health hazard to humans. However, exposure to the associated high volumes of audible sound can produce a variety of effects, including fatigue, headaches, nausea, and tinnitus. When ultrasonic equipment is operated in the laboratory, the apparatus must be enclosed in a 2-cm-thick wooden box or in a box lined with acoustically absorbing foam or tiles to substantially reduce... 

All pressure equipment should be tested or inspected periodically. The interval between tests or inspections is determined by the severity of the usage the equipment has received. Corrosive or otherwise hazardous service requires more frequent tests and inspections. Inspection data should be stamped on or attached to the equipment. Pressure vessels may be subjected to nondestructive inspections such as visual inspection, penetrant inspection, acoustic emissions recording, and radiography. However, hydrostatic proof tests are necessary for final acceptance. These tests should be as infrequent as possible. They should be performed before the vessel is placed in initial service, every 10 years thereafter, after a significant repair or modification, and if the vessel experiences ovrapressure or overtemperature. 

A loss control measure against identified risks by segregating the identified hazard to a specific (remote) location to protect the surrounding area from its effects and vice versa. Examples include placement of a chemical plant or process in a remote location and enclosure of an individual in an acoustic booth or enclosure to protect against noise exposure. 

Intrinsically safe - acoustic emission transducers are often rated intrinsically safe so that they can be installed in a hazardous area without the need for purged or explosion-proof enclosures. This makes deployment easy in locations such as petrochemical plants. 

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