Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration

Our plain-English summary of Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration, by I. Kulmala, M. Linnainmaa, A. Kokkonen, et al (Annals of Work Exposures and Health, 2021).

The study

• Authors: I. Kulmala, M. Linnainmaa, A. Kokkonen, K. Heinonen, T. Kanerva, A. Säämänen
• Journal: Annals of Work Exposures and Health
• Published: 2021;65(9):1085-1095
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The aim of the study was to find out good practices for effective air distribution inside a complex shaped asbestos enclosure and for control of pressure differences between the enclosure and the surroundings. In addition, sufficient pressure difference for asbestos containment was tested. The effect of air distribution was studied in laboratory conditions by constructing an L-shaped asbestos enclosure and connecting it to a negative pressure unit. The efficiency of six different ventilation configurations was compared using a tracer decay method and the local air change indexes as the performance indicator. The sufficient negative pressure for containment was assessed by simulating person traffic to and from the enclosure and recording the pressure difference continuously. The effect of a pressure controller unit in maintaining the target pressure difference was also tested by simulating filter loadings of the negative pressure unit causing changes in the air flow rate. The results showed that high nominal air change rates alone do not guarantee good air distribution. Effective air distribution within an asbestos enclosure can be arranged by locating additional air supply openings far away from the air exhaustion point, using recirculation air with a pressure controller, or extending the exhaust location to the poorly ventilated areas. A pressure difference of at least -10 Pa is recommended to ensure a sufficient margin of safety in practical situations.

© The Author(s) 2021. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

In plain English

This laboratory experiment, run by Finnish research institutes, tested ventilation of an awkwardly shaped asbestos removal enclosure; no asbestos was used. The authors built an L-shaped plastic enclosure (32 m3) with a three-chamber airlock. They released DEHS test particles and measured how fast they cleared at two points under six ventilation set-ups, each run three times. Mixing was poorest (mean local air change index 64%) when replacement air came only through the airlock and exhaust was near it. A second air inlet, filtered air returned through a pressure controller, or a hose moving the exhaust into the poorly ventilated compartment improved air exchange; the hose set-ups averaged clearly over 100%. Starting from 10 Pa negative pressure, a person entering lowered the difference to −5 Pa; starting from −5 Pa, entries lowered it to between −1.4 and −2.9 Pa. During simulated filter clogging, pressure with a controller fluctuated somewhat but averaged −10 Pa. The authors concluded that high nominal air change rates alone may not guarantee good air distribution, and recommended at least −10 Pa.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory experiment comparing ventilation configurations in a mock-up asbestos enclosure, using a particle tracer decay method
• Who was studied: one L-shaped enclosure (floor area 16 m2, volume 32 m3) built of timber frames and polyethene sheeting with a three-chamber airlock, inside an office room; six ventilation configurations, each measured three times; no people inside during the ventilation measurements
• Exposure: no asbestos fibres were used; submicron di-ethyl-hexyl-sebacate (DEHS) test particles served as a tracer under different supply and exhaust arrangements, at nominal air change rates of 10 and 19 per hour; pressure tests simulated person entry and exit and filter loading of the negative pressure unit
• Main results:
  • Case A (replacement air only through the airlock, exhaust near the airlock): local air change rates were 5.6 and 7.1 per hour at the two measuring points, below the nominal 10 per hour; the mean local air change index was 64%, the lowest of all cases
  • Case B (about half of the replacement air through a filtered opening in the enclosure wall): the local air change rate exceeded the nominal rate at both measuring points
  • Cases D and E (exhaust moved by hose into the poorly ventilated compartment) gave the highest local air change indexes, with a mean clearly over 100%, which the authors interpreted as a displacement or piston flow type air flow pattern
  • With the pressure difference set at 10 Pa before passage, the lowest pressure difference during person entry was −5 Pa
  • With an initial pressure difference of −5 Pa, the lowest pressure differences were between −1.4 and −2.9 Pa during entries and between −2.4 and −2.6 Pa during exits
  • During simulated filter loading (G4 filter sheets added one per minute), the pressure difference fell steadily when the negative pressure unit exhausted directly outdoors; with a pressure controller, the pressure fluctuated somewhat but its mean stayed at the target of −10 Pa
• The authors' conclusion: The authors concluded that high nominal air change rates alone may not guarantee good air distribution. They found that ventilation can be improved by additional supply openings, recirculated air with a pressure controller, or extending the exhaust to poorly ventilated areas. They recommended a pressure difference of at least −10 Pa.

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