Page 449 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

430 14 Indoor Air Quality

Formaldehyde has been produced by catalytic oxidation of methanol for over
two centuries [5]. It is widely used for the production of resins. Formaldehyde-
based resins are used as adhesives in the manufacturing of construction materials,
such as plywood, particle-board, and moulding materials. They are also used for
furniture and other wood products. It is also a raw material for surface coatings,
leather, rubber, and cement industries. Other indoor sources include stonewool and
glasswool mats in insulating materials [6].
It is not clear how many people are occupationally exposed to formaldehyde
worldwide. However, there are three types of occupations that are of high risk. The
first is those working in the production of aqueous solutions of formaldehyde and
their downstream chemical industries such as the synthesis of resins. The second
group is related to its release from formaldehyde-based resins during the manu-
facture of wood products, textiles, synthetic vitreous insulation products, and
plastics. Last but not the least, people are exposed to the pyrolysis or combustion of
organic matter, e.g., in engine exhaust gases.
Indoor volatile organic compounds (VOCs) are emitted by many indoor mate-
rials. They can be generally grouped into two, being building materials and daily
consumable products. Building materials include adhesives, glues, furniture fin-
ishing, sealants, paints, stains, varnishes, wood preservatives, new carpet dyes and
fibers, and plastics. The daily consumable products include air fresheners, per-
fumes, hairsprays, hair gel, cleaning solvents, shoes and fabrics, automotive
products, and contaminated water in sewage and sink.
Indoor air quality is a comprehensive topic that requires multiple disciplines,
including, almost all branches in modern science and engineering. In this chapter,
we focus on the engineering basics and technologies for indoor air quality control.

14.2 Threshold Limit Values

Threshold limit values (TLVs) refer to the upper limit of the concentrations of
indoor air pollutants under which it is believed to be safe for all working occupants
without impacting their health. The TLVs are established for different substances
mainly for protecting the occupants’ health with some tolerance of the discomfort
such as irritation, narcosis, nuisance, or some stress. Examples of the health
impairments that the TLVs are set against include compromise physiological
function, adversely affect reproduce developmental processes, and shorten life
expectancy.
There are two categories of TLVs. One is issued by governmental regulatory
agencies and enforced by law; the other is published as recommended guidelines by
scientific communities. For example, in the US, the former is defined by the
Environmental Protection Agency (EPA) and the Occupational Safety and Health
Agency (OSHA) of the United States; while the later can be set by America
Conference of Governmental and Industrial Hygienists (ACGIH), American