Carbon monoxide poisoning associated with blasting operations close to underground enclosed spaces. Part 1. CO production and migration mechanisms

Abstract

Explosives used for blasting operations in civil engineering works can generate large volumes of carbon monoxide (CO). The production of 10–24 L of CO per kilogram of explosives blasted is theoretically possible. CO can migrate a considerable distance in the fractured rock of the blasted areas and then infiltrate closed spaces (sewage systems, manholes, basements of houses). In the Province of Quebec, in the last 10 years, seven people were poisoned by CO in their houses to the extent that they had to be treated in a hyperbaric chamber. Underground conduits broken by blasting, filling around underground conduits in road or house trenches, or fractured rock created by blasts between houses or between a house and a road are the different CO pathways identified in the Quebec incidents. Field tests done by our group show that (i) the structural geology of the rock formation (schistosity, family of joints and fractures) controls the direction and extent of gas migration in fractures generated by blasts; (ii) the confinement of the rock can affect the quantity of gas migrating in the fractured rock; (iii) significant concentrations of CO may persist in the fractured rock 7 days after a blast; (iv) advection is the initial mechanism of CO migration immediately after a blast, and the distance of migration varied from 8 m in the fractured rock to 20 m in the fills of a road trench; and (v) further CO migration by diffusion up to 15 m in the induced fractures and 30 m in fills may occur in the 3 days following a blast.Key words: carbon monoxide, blasting, poisoning, enclosed spaces, gas migration, house.