1990年6月1日，由T.C.5.6《消防和烟雾控制》赞助的研究项目（RP-660）启动，题为“确定防止楼梯门开口处烟雾回流的临界风速”。本提案的目的是确定非火灾条件下的临界速度，以防止在不同火灾温度下，火灾楼层上打开楼梯门处的烟气回流，通过外墙通风口或排气扇对火灾楼层进行通风，向楼梯井多次和底部注入送风，以及对许多打开的楼梯门进行通风。本研究项目是ASHRAE研究项目RP-559“楼梯间增压系统过压释放方法研究”的后续项目后一个项目的目标是评估楼梯间增压系统，包括出口门安全阀、气压风门安全阀和带反馈控制的可变供气系统。 在进行该研究项目时，很明显，设计楼梯增压系统需要更全面的临界空气速度数据，尤其是在低温和其他火灾条件下。

The research project (RP-660) entitled "Determination of Critical Air Velocities to Prevent Smoke Backflow at Stair Door Openings" sponsored by T.C. 5.6, Fire and Smoke Control was started on June 1, 1990. The objectives of this proposal were to determine critical velocities at non-fire condition that prevent smoke backflow at open stair door on the fire floor for various fire temperatures, venting of the fire floor either with exterior wall vents or with an exhaust fan, multiple and bottom injections of supply air to the stairshaft, and for a number of open stair doors.This research project is a follow-up of the ASHRAE research project RP-559 entitled "To Study Methods of Over- Pressure Relief for Stairwell Pressurization Systems." The objectives of the latter project were to assess stairwell pressurization systems with exit door relief, barometric damper relief, and variable supply air with feedback control. While carrying out this research project, it became apparent that a more comprehensive data on critical air velocities particularly at low fire temperatures and other fire conditions were required for designing stair pressurization systems.