Even the smallest of gaps will allow smoke, toxic gas, heat and even flames to pass, and fire stopping — also known as penetration sealing — is the process of making sure that this doesn’t happen or is, at the very least, considerably slowed. Buildings are constructed under fire codes, which include constructing walls, ceilings, barriers, and floors in a certain way as to act as passive fire protection systems. However, utility systems consisting of ducts, pipes and cables live within a building, penetrating these structural barriers and compromising its fire protection integrity. Sealants, compounds, etc. help stop these potential hazards, and this practice is (now quite obviously) called fire stopping.