MIL-HDBK-116, MILITARY HANDBOOK ENVIRONMENTAL CONTROL OF SMALL SHELTERS (30 JUN 1989)., The content addresses procedures for determining the type and size of environmental control units (ECU) required, methods for installing ECU's and distribution of conditioned air in shelters. Nuclear, biological, and chemical (NBC) equipment and its use with the ECU and steps that might help the ECU to survive and function in an NBC environment are also addressed briefly.