A penetration, in firestopping, is an opening, such as one created by the use of a cast-in-place sleeve, in a wall or floor assembly required to have a fire-resistance rating, for the purpose of accommodating the passage of a mechanical, electrical or structural penetrant. The penetration may or may not contain a firestop system. A penetration is not a penetrant. A penetration may or may not include a penetrant. Images See also Sleeve (construction) Passive fire protection Annulus (firestop) Joint (building) Penetrant (mechanical, electrical, or structural) Mortar (firestop) Firestop pillow Fire test External links Penetration seals (firestops) treatise by Warrington labs Penetration seals (firestops) treatise by Nuclear Regulatory Commission Penetration seal (firestop) vendor listings by Thomas Register Passive fire protection Building engineering Firestops