Though it’s arguably unwise to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps.

One of the oldest and more popular ballpoints were the Bic Cristal who originally made it part of their design to include a small hole at the end of the cap. Considering that pen caps were one of the common objects swallowed by children causing them to choke and proved fatal, the hole was put in to allow passage of air in case the dreadful event happened.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard.

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