| 摘要 |
A known powered air-purifying respirator has an alarm that is preset to be actuated whenever a Pitot static sensor indicates that the airflow has dropped below a safe level. The invention permits such a respirator to be used with either a tight-fitting facepiece or with a loose-fitting hood or helmet and, without adjusting the preset alarm, can indicate that the airflow has dropped below the proper minimum for whichever is being used. This is accomplished by supplying the respirator with two breathing tubes, a first of which is unobstructed and can be fitted only to a loose-fitting hood or helmet that required high airflow. The other breathing tube can be fitted only to a tight-fitting facepiece and has a protuberance that reduces the cross-sectional area of the chamber in which the Pitot static sensor is mounted so that the alarm is actuated only when the airflow drops below a level that is lower than the alarm-sounding level when the first breathing tube is being used.
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