Dust generation

Exposure to PTFE can arise from ingestion, skin contact, or inhalation. The polymer has no irritating effect to the skin, and test animals fed with the sintered polymer have not shown adverse reactions. Dust generated by grinding the resin also has no effect on test animals. Formation of toxic products is unlikely. Only the heated polymer is a source of a possible health hazard (120). 

Polyurethanes. These polymers can be considered safe for human use. However, exposure to dust, generated in finishing operations, should be avoided. Ventilation, dust masks, and eye protection are recommended in foam fabrication operations. Polyurethane or polyisocyanurate dust may present an explosion risk under certain conditions. Airborne concentrations of 25—30 g/m are required before an explosion occurs. Inhalation of thermal decomposition products of polyurethanes should be avoided because carbon monoxide and hydrogen cyanide are among the many products present. 

Depending on the feed materials, the dust generated during operation may be hazardous because of possible emissions and toxicity. These hazards must be carefully evaluated before proper design of the facility and selec ting the apparatus. 

Use of a vacuum cleaner or damping techniques to minimize dust generation. 

It is important to note that EAF dust is a hazardous waste because of its high concentrations of lead and cadmium. With 550,000 tons of EAF dust generated annually in the U.S., there is great potential to reduce the volume of this hazardous waste. The motivation for reducing this waste not only lies with the cost of air pollution controls, but with the cost for disposal. U.S. 

For processes that generate particles (dust, mists, fumes, etc.) there is no general procedure to calculate the contaminant s velocity and flow rate. Data and figures exist for some processes de.scribing the contaminant generation process however, for dust-generating processes Method B or C is often used. 

Commercial products do exist that integrate shrouded and ventilated grinding wheels and other hand-held tools. It may be possible to find an existing LVHV-type product that will work well for some applications, requiring only to be connected to an appropriate air handling system. However, it is also sometimes necessary to make custom-fabricated LVHV nozzles for some hand-held tools and for essentially all fixed-machine dust-generating tools. I he best approach is to consider the following ... 

As with any hood system, design methods are used to obtain required exhaust rates and hood dimensions.The main mechanisms of dust generation are air induction, material splash, air displacement, and air entrainment. 

Cost-effective control of dust problems arising from bulk materials handling requires an initial examination of the overall handling operations. Factors influencing dust generation and dispersion must be understood in order to achieve a proper design. 

A number of steps can be taken to minimize dust generation and dispersion. For the clamshell case, an active containment design was pursued to minimize dispersion. Active containment relies upon an inflow of air into some type of enclosure. 

FIGURE 10.86 Practical application to remove dusts generated during handwork. Depth of the system is 6 m, supply airflow rate is 4.95 m s", and exhaust flow rate is 9.08 m s . ... 

Dust suppression The preventive measures taken to eliminate or reduce the spread of dust generated by a process into surrounding areas. 

The toxic effects of mercury have long been known,and the use of HgCl, as a poison has already been mentioned. The use of mercury salts in the production of felt for hats and the dust generated in ill-ventilated workshops by the subsequent drying process, led to the nervous disorder known as hatter s shakes and possibly also to the expression mad as a hatter . 

This operation is also performed using machines. The cured plates are fed into the parting machine by mechanical means. The plates are parted in the machine and then collected when the operation is completed manually. The parted plates are thereafter stacked for use in battery assembly. More rejects are also generated in this section as well as some lead dust. The ventilation system in this area ensures that the lead dust generated is removed from the work area and discharged into the atmosphere through a baghouse filter. 

A cloud of zinc dust generated by sieving the hot dried material exploded violently, apparently after initiation by a spark from the percussive sieve-shaking mechanism... 

Heat losses due to dust generation and furnace geometry Gou et al. (1993) Ibaraki et al. (1995b)... 

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