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Quantifying Air Speed in an Isolated Subsurface Structure and Ventilation and Repair of a Dead-Ended Sewer Line (AIHce EXP 2023 OnDemand)

Course Description:
Recorded at AIHce EXP 2023

In this session, two unique confined space entries will be presented: 1) repair of a dead-ended section of a sewer line; and 2) quantifying air movement inside an isolated subsurface structure through openings in the manhole cover. In the first situation, groundwater penetration through the concrete pipe bulged inward the liner of PVC requiring a repair. The repair required: a) entry to remove the water; b) drilling through the concrete wall to inject fast-setting polyurethane foam; and c) hot-air welding to repair the PVC. Assessment documents considered: 1) the emission of isocyanates and degradation products from the PVC; and 2) control using ventilation by calculating the number of fans needed to provide air flow in the most efficient geometry. Preparation of these documents provides a disciplined way to minimize the risk of performing work in these workspaces. In the second situation, small puffs of artificial smoke visualized the air movement inside an isolated subsurface structure through opening(s) in the manhole cover. Motion capture/analysis videos followed movement of the artificial smoke. Motion capture requires: a) access to individual frames in the video sequence; and b) a very slow frame rate. Motion analysis requires the means to: a) subtract unnecessary background; b) manipulate color, brightness, and contrast; c) measuresure distance from beginning to end of a sequence. An open-source physics program provided this capability. Air flow along the ground was borderline turbulent. Inside the structure flow was laminar.

Learning Outcomes:
Upon completion of the session, the participant will be able to:

• Use motion capture/analysis software to determine air speed of a puff of smoke.
• Determine airspeed along the ground and within a structure.
• Apply the method and motion capture/analysis software to other airflow studies.
• Discuss a strategy for planning multitask work in a confined space.
• Describe how to approach individual tasks by dissecting them into elements as needed.
• Assess hazardous conditions using industrial hygiene strategies.
• Identify external resources useful for assessing hazards and creating control strategies.
• Leverage the external resources to assess the situation specific components.

Contact Hours:

Presentation Date:

Warren Brown, CSP, ARM, CSHM, FASSP
Neil McManus DSc., CIH, ROH, CSP