Weather   Climate    Water

Commission for Instruments
and Methods of Observation

draft version; updated: 2010-02-12


Mercury [Hg]

How to prevent severe illness and to protect the environment

Why do we use mercury?

Listening to the weather forecast you can often hear that ‘the mercury will raise to tropical levels’ or even more curious that ‘the mercury will drop below zero’ to warn for freezing. Also atmospheric pressure is reported in terms of ‘the barometer will fall below 30 inches of mercury’. All these expressions refer to thermometers and barometers where the use of mercury was common practice for ages.

Mercury, also known as quicksilver, is in common practice for several ages. It is a very remarkable heavy metal in particular because it’s a fluid and not a solid like the other metals at room temperature. Moreover also because of its significant cohesive behavior and high density of more than 13 times that of water mercury is an ideal material for many applications. Remember that Evangelista Torricelli used mercury already in the 17th century to demonstrate the mass of the atmosphere.

Although mercury is very useful, inhalation of mercury vapor will cause severe illness and some chemical compounds containing mercury are extreme toxic. To stay alive one should avoid frequently eating of fish containing a high level of mercury-based compounds.

Should we stop using mercury-in-glass devices?

So, as long as mercury remains inside a thermometer or a barometer, not directly in open contact with the air which we all breeze there is no reason to worry for our health. However, if a mercury-in-glass falls and breaks, or when a mercury filled barometer leaks then that’s a serious incident and appropriate actions should be carried out to reduce any impact. Moreover any spilled mercury will pollute the environment resulting in long-term serious impact. Not only due to a high concentration of toxic mercury vapor but also because in time the mercury will react with other chemical compound giving particular toxic compounds like within fishes. Also open bottles with mercury or vacuum pumps used with mercury-based calibrations standards, with non-filtered outlets must be regarded as very dangerous. Therefore the use of mercury-in-glass thermometers and barometers should strongly be discouraged. Moreover it should be avoided without any restriction that those instruments or any spilled mercury rests will go with the daily trash. Protection of the environment by preventing mercury-polluted waste is first priority for the health of mankind.

How to protect ourselves against direct contact with mercury vapor?

Today many laboratories follow strict regulations on the use of mercury. There are well-documented procedures, especially in those accidents with broken glass and other cases when mercury is spilled. In all cased special removal kits are prescribed preventing any loss of mercury, which will evaporate afterwards. Moreover special regulations and services exist to remove and store mercury at save places.

Where can I find appropriate information and recommended procedures?

Through the world wide web (commonly called internet) using the popular searching services one can find easily all type of information on safety and policy issues. Trying words like ‘mercury’, ‘safety’, ‘illness’ and ‘pollution’ will give an interesting amount of websites giving sufficient details in many languages. Not only information on recommended common practices for the use of mercury, but also what to be done with the removal of bottle of mercury or mercury filled devices. While searching the web a number of very informative documents were found and selected considered to be useful for observers of meteorological instruments containing mercury.



Symbol(s) and Indication(s) of Danger:


Dangerous for the environment


In 1643 Evangelista Torricelli created a tube ca. 1 meter long, sealed at the top end, filled it with mercury, and set it vertically into a basin of mercury. The column of mercury fell to about 76cm, leaving a Torricellian vacuum above. As we now know, the column's height fluctuated with changing atmospheric pressure; this was the first barometer. (from: wikipedia)


Today, new mercury barometers are manufactured, but the production is discouraged world-wide

The well known sling psychrometer, in operational use on board VOS ships.

Always keep your Hg filled bottles closed, especially at room temperature above 30°C


Are there appropriate alternatives?

There are sufficient appropriate alternatives to measure air temperature (dry and wet bulb) and atmospheric pressure. Electrical digital transmitters are on the market as well as sensors, not requiring electric power. The best source for selecting such an alternative is the Guide to Meteorological Instruments and Methods of Observation, also well known as the CIMO Guide (WMO No. 8, WMO Geneva, 2006). More details on this Guide can be found on the web at:




The CIMO Guide recommends appropriate alternatives


How to Clean Up Mercury Spills?

A number of useful site are available with good advises to clean up any mercury spill and safe disposal of mercury products:

Many websites provide good advices to clean Hg spills 




Are there activities going on to promote the reduction of use of mercury?

General information on (inter)national activities to reduce the use of mercury can be found via the following websites:


Programmes organized by international organizations help to reduce mercury in daily live:




European Commission

U.S. Department of Commerce





Where to find some general safety issues and tips?

A large number of well informative sites are available world wide, such as:


Many national organizations, universities and institutions provide advises and procedures on safety with mercury




Environment Canada





processed for WMO/CIMO at KNMI, NL (2008); photographs by J.P. van der Meulen (KNMI, 2008)