Development of new Device for Measurement of Airborne Fiber Concentration

Devices for the measurement of airborne fiber concentration currently existing on the market show significant disadvantages. Due to e.g. multi-step measurement principles or bulky design, existing devices are not capable to be used for specific applications. Knowledge of airborne fiber concentration is essential to determine operation conditions and air quality in e.g. textile mills, museums or operating rooms in hospitals. This paper presents a new measurement device according to VDI standard 2221. The device consists mainly of a converging duct, an exhaust system and an optical sensor. Preliminary trials prove the functionality of the developed fiber measurement system. INTRODUCTION According to [1] fibers are defined as long stretched particles with the following characteristics: • Length L > 5 μm • Thickness T < 3 μm • Length / thickness ratio L:T > 3:1 The measurement of airborne fiber concentration is essential for determination of air quality. For example the former use of asbestos as construction material did show that there is a need of an adequate measurement system. Inhalation of asbestos fibers can cause lung diseases such as asbestosis or lung cancer as well as a special type of breast cancer or peritoneum (mesothelioma) [2]. Therefore, the exposure of the population by airborne asbestos fibers must be kept as low as possible. Although the natural release of asbestos fibers from rocks cannot be controlled, it is possible to prevent the release of the fibers into the air, or to reduce it in the technical usage of asbestos fibers. Also in textile factories, airborne fibers lead to the pollution of objects and clothes and can irritate the skin or interfere with breathing. For certain substances there is a risk of allergies, poisonings or cancer. Also textile mills processing carbon fibers need to know about the amount of airborne carbon fibers since this fiber material is highly conductive [2]. Moreover, visitors’ clothing can be a source of fibers and dust in museums [3] [4] or operating rooms in hospitals and therefore affect the air quality. For that reason, this paper will present an easy to handle device for the measurement of airborne fiber concentration. STATE OF THE ART A principle to determine airborne fiber concentration is based on VDI standard 3492 [5]. Here the air flow is lead through a specially designed sampling device. The sampling device consists of a gold-sputtered capillary pores membrane filter made of polycarbonate. The gold layer is required primarily for the dissipation of electric charge while a scanning electron micrograph image of the filter is made. The gold layer ensures that there is no change of the geometric dimensions of the fibers which are collected on the filter during the examination. The intake of air itself takes about eight hours and is followed by an SEM examination of the mentioned filter. Thus it is manually investigated whether the intake of air through the filter led to depositing of fibers on its surface. For this purpose, the SEM image of the filter is enlarged by a factor of 2000 to count the fibers and to measure the corresponding fiber length. Counting of the fibers follows special rules published by the World Health Organization [6]. Fiber concentration C is calculated with the following information: • Result of fiber counting • Surface area of the filter medium • Analyzed volume of air Finally, fiber concentration C results from: