ISO 11540:1993

Caps for writing and marking instruments intended for use by children up to 14 years of age — Safety requirements

Specifies safety requirements for cap size, ventilated caps (vent area, air flow) and marking. Annex A describes the test for air flow. Caps which do not comply should have the instrument or its packaging labelled with a warning as to the dangers of asphyxiation from pen caps.