Reduced time exposure

General strategy for control (Control of Substances Hazardous to Health Regulations). Identification of a hazard. Assessment of risk. Choice of control measures (including process change, substitution, segregation, engineering controls, reduced time exposure, personal protective equipment). 

This involves reducing the time during the working day that the employee is exposed to the hazard, either by giving the employee other work or rest periods. It is only suitable for the control of health hazards associated with, for example, noise, display screens and hazardous substances. However, it is important to note that for many hazards there are short-term exposure limits as well as normal working occupational exposure limits over an 8-hour period (see Chapter 16). Short-term limits must not be exceeded during the reduced time exposure intervals. 

In addition to reduced time exposure of employees to the noise source, there is a simple hierarchy of control techniques ... 

Time involves the use of the reduced time exposure principle and thus reduces the accumulated dose. 

Perhaps the greatest stimulus for the development of such tools has been the proliferation of high angle wells in which deviation surveys are difficult and wireline logging services are impossible (without some sort of pipe conveyance system), and where MWD logging can minimise formation damage by reducing openhole exposure times. 

The Occupational Safety and Health Act (OSH Act) was enacted by Congress in 1970 and established tlie Occupational Safety and Health Administration (OSHA), which addressed safety in tlie workplace. At tlie same time tlie USEPA was created. Both USEPA and OSHA are mandated to reduce tlie exposure of Itazardous substances over Umd, sea, and air. Tlie OSH Act is limited to conditions that exist in the workplace, where its jurisdiction covers both safety and health. Frequently, both agencies regulate tlie same substances but in a different manner as they are overlapping environmental organizations. 

The ideal of any vaccine is to provide life-long protection to the individual against disease. Immunological memory (Chapter 14) depends upon the survival of cloned populations of small B and T lymphocytes (memory cells). These small lymphocytes have a lifespan in the body of ca. 15-20 years. Thus, if the immune system is not boosted, either by natural exposure to the organism or by re-immunization, then immunity gained in childhood will be attenuated or lost completely by the age of 30. Those vaccines which provide only poor protection against disease have proportionately reduced time-spans of effectiveness. Yellow fever vaccination, which is highly effective, must therefore be repeated at 10-year intervals, whilst typhoid vaccines are only effective for 1-3 years. Whether or not immunization in childhood is boosted at adolescence or in adult life depends on the relative risks associated with the infection as a function of age. 

OSHA requires employers of workers who are occupationally exposed to a toxic or hazardous substance to institute engineering controls and work practices that maintain or reduce their exposure to a level that is at or below the permissible exposure limit (PEL) established for the substance. For occupational exposures to lead, the employer must use engineering controls and work practices to achieve an occupational exposure of 50 pg/nr3 (0.006 ppm) or lower, based on an 8-hour time-weighted average (TWA) (OSHA 1995). When employee exposures to lead can not be maintained at or below 50 pg/rn3... 

Levin, B.C. Paabo, M. Gurman, J.L. Clark, H.M. Yoklavich, M.F. Further Studies of the Toxicological Effects of Different Time Exposures to the Individual and Combined Fire Gases-Carbon Monoxide, Hydrogen Cyanide, Carbon Dioxide and Reduced Oxygen, Polyurethane 88. Proceedings of the 31— SPI Conference. Philadelphia, PA, 1988, p. 249-252. 

Time-Resolved Crystallography. Time-resolved crystallography (TC) uses an intense synchrotron X-ray source and Laue data collection techniques to greatly reduce crystallographic exposure times. Normal time resolution for X-ray... 

Figure 9 shows the DMTA curves neasured after various irradiation times. On reducing the exposure time from 600 to 0 seconds the maximum in tan 5 shifts progressively towards lower temperatures. For exposure times of 5 s and less, thermally induced... 

Time-resolved x-ray crystallography (TC) is a more recent advanced application of x-ray crystallography. It uses an intense synchrotron x-ray source and data collection methods to reduce crystallographic exposure times. This allows multiple exposures to be taken over time at near-physiological, crystalline conditions to determine the structures of intermediates. A typical problem with this method is that the existence of the intermediates is brief, resulting in difficulty in interpreting the resulting electron density maps. 

The expression 10 6, commonly used in sterilization validation, is the B term in Eq. (11). What this means is that after an equivalent time-exposure period of FT units, the microbial population having an initial value of A has been reduced to a final B value of 10 6. Statistically, this exponential term signifies that one out of 1 million units of product theoretically is nonsterile after sterilization exposure of Ft units. For example, if 106 micro-organisms having a D value of 1 min at 121°C are placed in a container and the container exposed to 121 °C for an equivalent time of 12 min... 

The work to be reported on here involves an approach of treating normal clothing in order to achieve a level of protection through repellency. It was reasoned that resin treated textile might be repellent to sprays, hence reducing dermal exposure. At the same time, it was hope that the woven textile might retain... 

Ventilation is often adopted as a control measure to keep VOCs and C02 below specified threshold levels. The effect of operation of the ventilation system on spatial and temporal profiles is illustrated from two separate buildings. With adequate ventilation, the C02 levels are easily controlled within threshold levels. However, VOCs present a problem due to their build-up overnight between the time of ventilation shutdown after office hours and its reactivation in the morning just before occupancy. Purging the building as an effective means to reduce the exposure risks is discussed and illustrated. Some concluding remarks on other changes to indoor exposures are made at the end of the chapter. 

Various surface analysis techniques show that silicate glasses rapidly develop surface compositional profiles when exposed to water. When water is present as a vapor an alkali-rich layer (presumably a hydrated alkali carbonate) forms over the SiOj-rich layer. Water as a liquid dissolves the alkali and leaves the silica-rich film. As long as this SiC -rich film is stable the rate of corrosion due to diffusion is reduced with exposure time. Addition of multi-valent species to the glass or reactant results in formation of a complex protective surface layer in the glass which may be stable over a wide range of environmental conditions. 

This requires numerical integration. As pointed out at the outset, these estimates of the mass transfer performance are likely to be conservative as the disturbance of the film by ripples has been neglected. This will reduce the exposure time significantly, particularly with inviscid liquids. 

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