Catalog · Physics of COVID-19 Transmission Lecture 27 of 49 Video 4-1: Safety Guideline for COVID-19—Cumulative Exposure Time ← Previous Video 4-0: Safety Guideline for COVID-19—Chapter 4 Overview Next → Video 4-2: Safety Guideline for COVID-19—Transmission Rate ✓ Mark complete Materials Transcript (PDF) ↗ transcript