A video showing a man demonstrating how to quickly block a classroom door with a chair in an active shooter situation has gone viral this week, igniting a debate about school safety in the wake of the massacre in Uvalde, the NY Post reports. Robb Beaux tweeted the 45-second “life hack” video Sunday, in which a man in a reflective work vest gave a demonstration with a plastic-and-metal school chair.

In the recording, the man instructs his audience off camera to put a tennis ball, “some glitter, or googly eyes” on the back left leg of the chair, so that everyone knows that it is the leg needed to block the door. The instructor then picks up the chair, wedges the back left leg into the door handle, and twists the chair backwards, leaving it suspended.

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