September 2009 - Mercury-vapour bulbs: obviously "very dangerous, as they contain mercury"!

In the 60s, as Student Engineers, we had to determine the melting point of the crystals of organic molecules that we synthesized. The higher the melting point, the purer the synthesized product. Besides the KOFLER hot bench, we used a "mercury bath" on the surface of which we put some crystals. We recorded the mercury temperature when crystals melted. This mercury bath was heated by a Bunsen burner flame. A temperature above 120°C (248°F) was not unusual and, our noses being very closed, we inhaled mercury vapours. We were well-informed and knew the risks, but ... it was the way of life!

We could not proceed this way nowadays!

This is a short story, just to make think twice before deciding what seems to be a good action as per Health and Safety (H and S) concerns.

Mercury-vapour bulbs have been used since decades--in fact, since ca 1880, as a reliable source of UV radiation (UV-A, UV-B, or UV-C mainly, depending on the pressure in the bulb while "ON", due to the quantity of Argon put in when manufactured). They are also often used as "white light" sources in large buildings such as stores, manufacturing lines, or in outside car-parks, etc.

These bulbs contain a small amount of mercury. Mercury is a liquid metal at room temperature. As a liquid, if let in an open tank, it emits vapour. Mercury may react with a lot of organic molecules (carbon-based molecules). When ingested by microscopic living fauna such as that living in rivers, seas, etc, then when these microscopic living bodies are ingested by a bit larger animals, which themselves are eaten by still larger ones, etc, mercury accumulates along the food chain. When "larger ones" are human beings eating fish, it may happen that mercury doses lead to health troubles (the Minimata or Minamata disease in the '50s: due to the bioaccumulation of methylmercury).

Mercury in the vapour form is rarely a problem: mercury is always used in closed containers.

And this is exactly the situation with UV-A bulbs used in the NDT applications! Mercury is in a sealed glass. Impossible to be in contact with it ... unless the bulb is broken.

So we were very surprised some few years ago, when we got an emergency phone call from people using UV-A bulbs for leak detection on cars engines in the plant of a very large car manufacturer. "Please, tell us what we must use, as mercury-vapour bulbs use is forbidden from now -- we have been advised one hour ago!"

We had to go to the plant, to meet users, to meet Health and Safety Committee people, to give all the explanations, and make them understand that using such bulbs is ABSOLUTELY safe, as far as these bulbs are not broken.

Some suppliers went with Xenon-based systems, stating that using them would solve the problem. But ... these suppliers did not know -- probably; but they should have known! -- or did not say the users- a lie!- that there is a small amount of mercury even in the Xenon bulbs!

Before writing a "diktat", better to ask people better informed about regulation, about what is technically achievable, at which price, etc.

We had a similar problem with a European Directive about some surfactants, the Alkyl phenol ethoxylates (whose abbreviation comes as ... APEs). This Directive was wrongly interpreted by some very large users as banning the APEs use in any circumstance. A thorough reading, a better understanding, a closer cooperation with the suppliers would have lowered by far the consequences of the "diktat": "no more APEs in the chemicals we use in our company, target date: 4 months from now". This will probably be the topic of an other paper.