p.213 in Henry and Heinke. Dust is removed from the airstream of a municipal inc
ID: 1828065 • Letter: P
Question
p.213 in Henry and Heinke.
Dust is removed from the airstream of a municipal incinerator by four dust collectors operating in parallel, each handling 1/4 of the total airflow of 200 m3/min. The airstream contains 10 g/m3 of suspended solids. The collector efficiency is 98%, decreasing linearly to 74% as air flow is doubled. If the maximum permissible solids concentration from the combined stack discharge [all 200 m3/min] is 1.0 g/m3, can one collector be temporarily taken out of service by: (a) overloading the other 3 units [i.e., each of the three handling 1/3 of the total flow], or (b) by not treating 1/4 of the airflow [i.e., mixing 150 m3/min of treated air with 50 m3/min of untreated air]?
Explanation / Answer
Airborne contaminants occur in the gaseous form (gases and vapours) or as aerosols. In
scientific terminology, an aerosol is defined as a system of particles suspended in a gaseous
medium, usually air in the context of occupational hygiene, is usually air. Aerosols may exist
in the form of airborne dusts, sprays, mists, smokes and fumes. In the occupational setting,
all these forms may be important because they relate to a wide range of occupational
diseases. Airborne dusts are of particular concern because they are well known to be
associated with classical widespread occupational lung diseases such as the pneumoconioses,
as well as with systemic intoxications such as lead poisoning, especially at higher levels of
exposure. But, in the modern era, there is also increasing interest in other dust-related
diseases, such as cancer, asthma, allergic alveolitis, and irritation, as well as a whole range
of non-respiratory illnesses, which may occur at much lower exposure levels. This document
aims to help reduce the risk of these diseases by aiding better control of dust in the work
environment.
The first and fundamental step in the control of hazards is their recognition. The
systematic approach to recognition is described in Chapter 4. But recognition requires a clear
understanding of the nature, origin, mechanisms of generation and release and sources of the
particles, as well as knowledge on the conditions of exposure and possible associated ill
effects. This is essential to establish priorities for action and to select appropriate control
strategies. Furthermore, permanent effective control of specific hazards like dust needs the
right approach to management in the workplace. Chapters 1 and 2, therefore, deal with the
properties of dust and how it causes disease. Chapter 3 discusses the relationship of
management practice and dust control.
1.1 Dust as an occupational hazard
According to the Interna
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