Ventilation of an Isolated Subsurface Structure Induced by Natural Forces

Thomas Neil Mcmanus,Assed Haddad

doi:10.3390/infrastructures4020033

Thomas Neil Mcmanus, Assed Haddad

Open Access

https://doi.org/10.3390/infrastructures4020033

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Abstract

The subsurface infrastructure comprises many types of isolated structures, a type of confined space. This study reports on the effect of engine operating time, number/area and spacing of openings in the manhole cover, and operation during different seasons on ventilation of a subsurface, isolated, pre-cast concrete chamber through opening(s) in the manhole cover. Carbon monoxide (CO) emitted by a small gasoline engine reached 800 ppm in 30 s at the start of testing. Ventilation occurred continuously. Generally, the concentration of CO reported by instruments located at different heights was the same for the same moment in time, suggestive of a rapidly well-mixed atmosphere. Mathematical modelling suggested that ventilation occurred through a zero-order kinetic process. Statistical testing suggested that optimization of ventilation is possible through design modifications such as change in the number/area/shape/spacing/geometric arrangement of openings in the manhole cover. Optimizing the rate of ventilation induced by natural forces during the interval between entries will reduce the risk of explosion of the confined atmosphere and overexposure of workers when opening the manhole cover to prepare for entry. This improvement will have immense implications to safety worldwide.

Highlights

The subsurface infrastructure is fundamental and essential to the functioning of modern cities and urban areas
Involvement of surface wind in creating a major contribution to ventilation of subsurface structures is considered in another forum [5]. These results support the contention that ventilation of isolated subsurface structures induced by natural forces occurs in a continuous and generally predictable way through manhole covers and access hatches having one or more openings
The results show that this ventilation supports the well-mixed box model; namely, that the atmosphere in the confined airspace mixes immediately, rapidly, and thoroughly with air entering through opening(s) in the manhole cover

Summary

Introduction

The subsurface infrastructure is fundamental and essential to the functioning of modern cities and urban areas. The subsurface infrastructure comprises many types of chambers and related components and piping broadly classifiable as open or isolated systems. Open systems contain structures interconnected by piping. The sanitary and storm water collection systems are examples of open systems in which flow of water occurs through piping between manholes and other structures. These systems can share the same atmosphere because of migration through the airspace above the liquid. Some subsurface structures are isolated from each other by design. The potable water supply system contains many examples of isolated subsurface structures. Isolation can involve sections of interconnected structures. Isolation of sections of interconnected structures is usually a temporary measure

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