Carried by government weather bureau or similar official agency.
These devices contain more mercury than consumer devices (see separate entry in this table for medical/clinical thermometers) and may only be carried by a representative of a government weather bureau or similar agency.
Must be in carry-on baggage only.
The individual must advise the airline of the presence of the mercury barometer or thermometer in the carry-on baggage.
Must be inside a strong outer packaging having a sealed inner liner or bag constructed of strong, leak-proof and puncture-resistant material that is impervious to mercury and will prevent the escape of mercury from the package in any position.
See the regulation: 49 CFR 175.10(a)(13)