I was up in the North East over the weekend for a family wedding. We stopped overnight and on the way home decided to visit the Souter Lighthouse at Whitburn. Opened in 1871 and operated until 1988, it is now owned by the National Trust. Standing in a dramatic location on the cliffs between the Tyne and Wear, it was the first lighthouse to be powered by electricity.
After looking round the living quarters and the working areas of the complex we were able to climb the tower, accompanied by a guide. It was a steep climb up a spiral staircase and then an almost vertical ladder. According the NT website for the property, there are 76 steps – but it seemed like more!
There was a good view of the coast from the top of the tower, but the main attraction for me was the lamp mechanism. There are actually two fresnel lenses, one on top of the other. The beam from the lower lens was white while the upper one gave a red light. The whole lamp assembly weighs over four tonnes. It’s supported on a bath of mercury, one and a half tons of the stuff, which has two purposes. First of all it keeps the lamp perfectly level. Secondly it makes it easy to rotate the lamp assembly by reducing friction. We were able to prove this for ourselves by pushing it around with our fingers.
A lighthouse fresnel lens (Source: Wikipedia)
Mercury, of course, is highly toxic, and the lighthouse keepers must have been exposed during their day to day activities, particularly when they had to remove impurities from the top of the bath and also when they had to periodically clean the liquid metal by passing it through a chamois leather, which they had to do every few months. Like most occupational hygienists I’m quite “sad”, I couldn’t help but wonder about what the lighthouse keepers were exposed to, so when I got home I did a search to find out whether anyone has done any work on tthis. I didn’t find much, just two relevant references.
A study on airborne mercury concentrations in lighthouses along with evaluation of urinary mercury levels was carried out in a lighthouse in Canada in the 1980’s by van Netten and Teschke of the University of British Columbia (1). The results from the air samples ranged from 4.4 to 26.3 μg/m3. We don’t have a WEL for mercury in the UK, but the ACGIH TLV is 25 μg/m3 , so the survey certainly suggested that there was some risk that the TLV could be exceeded. Swabs taken on surfaces indicated that there was considerable accumulation of mercury on surfaces in the area of the light rotation mechanism, and other areas in the lighthouse. Urinary levels, however, were relatively low at <4 μg/24 hr urine. The authors of the study concluded that “mercury levels in this lighthouse appeared to be under control through effective convective ventilation and employee awareness“. I couldn’t find any other studies, but I wonder whether this was typical of lighthouses in general. Today, lighthouses are usually automated and there is much less risk of exposure. However, the levels reported in the study by van Netten and Teschke from the 1980’s were certainly of concern and it is likely that in the past exposure was even higher.
The second paper I unearthed was particularly interesting. One of the main concerns with mercury is the effect on the central nervous system causing effects such as short-term memory loss, incoordination, weakness, confusion, and psychological changes including the manic behaviour associated with the “mad hatter”. The paper, by Michaela Walter of the University of Calgary (2) discussed the possibility of mercury exposure being the cause of “madness” amongst lighthouse keepers in Canada. According to this paper
“Keepers were not aware of the many dangers of mercury and did not wear protective gear in those days.Another prevailing factor was the amount of time they spent in the area where the lens and lighting system was kept. Keepers routinely cleaned and maintained the lens and mercury bath, lit and cleaned the lamp, as well as reset the gears every three hours t o allow the light to rotate. All of this additional time in the upper area of the lighthouse where the mercury bath was would have allowed for greater exposures to mercury vapour.”
Of course, psychological problems could be explained by other reasons – for example the pressures of working in an isolated location for long periods of time. However, her conclusion is that
“although difficult to substantiate, exposure to potentially toxic levels of mercury is a plausible explanation for the actions and behaviours displayed by lighthouse keepers during the early 1900’s on the West Coast of Canada.”
We’ve all heard the term “mad as a hatter”, often attributed to the incidence of psychological effects due to mercury amongst workers in the hat manuffacturing industry. Perhaps “mad as a lighthouse keeper” is an alternative!
1. van Netten and Teschke, Assessment of mercury presence and exposure in a lighthouse with a mercury drive system, Environmental Research Volume 45, Issue 1, February 1988, Pages 48-57
2.Lighthouse keeper’s madness: Folk legend or something more toxic? M Walter – History of Medicine Days