The last known case was in Britain in 1978 when a university photographer who worked above a lab handling smallpox died after being accidentally exposed to it from the building's air ductsystem.
The SPRD is used on zone systems when the automatic closing of various zone dampers can create an excessive increase in air pressure and velocity throughout the ductsystem.
SPRD旁通阀是当各种区域风门自动关闭时用在区域系统中，可以在管道系统中增加空气压力盒速度。
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The SPRD will automatically open as the air pressure in the ductsystem increases, in order to prevent the reduction of air flow and excessive noise and velocity through the ductsystem.