Gases

Definition

Elements and compounds in a dispersed physical state that do not resist changes to shape and can expand indefinitely to fill any container. The term is normally restricted to substances that are gaseous at ambient atmospheric temperatures and pressures (but volatile liquids, under ambient conditions, can produce vapours that enter mixtures of gases).

Synonyms

Airborne compounds; Atmospheric elements; Emissions; Vapours

Introduction

Gases of significance in engineering geology are potentially hazardous and can occur in significant amounts in underground cavities (natural and man-made), soils, landfills, and constructions at ambient temperatures and pressures. These normally occur as mixtures with atmospheric gases. Liquids that are volatile in surface and near-surface conditions (especially volatile organic compounds – VOCs) also enter mixtures of gases especially during heat and pressure changes. Therefore, hazardous “gases” originate from natural processes, human...