Respirators are not the same as surgical masks. Surgical masks do not protect against breathing in very small particles such as dust or mold because they do not fit tightly to the face, allowing air particles to leak in around the edge of the mask.
6. How long did it take to build the Great Wall in China? The Great Wall of China was built in several stages, not in one continuous effort. Beginning is the 6-7th century BC and ending in the 16th century AD. 7. How wide and how tall the Great Wall of China is? The Great Wall is wide enough at the top for five horses or ten men to walk side by side. The Great Wall ranges in height from just a few feet to over 30 feet tall. Since some of the Wall is built on mountain peaks and high ridges, it looks even taller. 8. What is the best time to visit the Great Wall of China?
Below we give you the background behind the figures, explaining what is counted as the Great Wall, and how the length of the Great Wall has changed through different dynasties. The Official Length: 21,196 km (13,170 mi) After a five-year-long survey, the total length of the Great Wall was measured. On June 5th, 2012, the State Administration of Cultural Heritage announced that the official length of the Great Wall is 21,196.18 km (13,170.7 mi). This is the first time that China has scientifically and systematically measured the length of the Great Wall. It's a misleading figure as some sections of different eras were built on top of or right next to each other.