That comes from Ian Walker, who set up a bicycle with sensors and drove around the city. Vehicles tend to crowd closer to him when he was wearing a helmet than when he wasn’t.

1mA of current through the human body can be felt, 10mA of current is sufficient to make muscles contract to the point where you cannot let go of a power source, and 100mA is sufficient to stop the heart.

the basic condition for the safety of masonry is that the thrust line is kept within the middle third of a wall or column

number of times material strength is higher than expected working load