Mercury vapor from blood pressure devices

[Swamp Thing]

TL;DR Summary

Some mercury vapor must escape from the manometer each time the cuff is inflated and deflated. How much of a health hazard is this?

I came across some articles about the health hazard from broken mercury-based sphygmomanometers. This led me to think about vapor leakage from good devices during normal operation.

The top of the glass tube is at ambient atmospheric pressure. There is supposed to be a membrane at the top that stops liquid mercury from spilling out (e.g. during transportation) but allows air pressure to equalize. So this means that each operation cycle pushes out some air that is saturated with mercury vapor. (This would be through the top membrane during inflation and through the deflating valve during deflation).

How serious would the risk be from this amount of mercury-saturated air that is being pumped out on each measurement cycle?

 

[BillTre]

They don't use those any more. There electronic now.
In normal modern use, the risk is zero. At least were I go.

In the past:
You want to find out the rate at which Hg will evaporate at room temp.
Then figure how the much atmosphere would be exposed to the evaporative surface in the manometer, and how it would get out of there to cause problems.
Seems pretty instrument specific.

 

[Swamp Thing]

If we aim for just a worst-case order of magnitude, we could assume that the Hg is at saturation vapor pressure before each operation cycle. If we assume a couple of cc of saturated air and maybe 20 cycles per day in a small office, would this be in the range where it becomes a concern for the staff members?

 

[russ_watters]

If we aim for just a worst-case order of magnitude, we could assume that the Hg is at saturation vapor pressure before each operation cycle. If we assume a couple of cc of saturated air and maybe 20 cycles per day in a small office, would this be in the range where it becomes a concern for the staff members?

Have you tried looking up the saturation pressure of gaseous mercury at room temperature and calculating what mass of mercury that is?

 

[Swamp Thing]

I did find this document where they directly give values for the saturated Hg concentration -- it's about 20 ng / cm^3.
https://www.sciencedirect.com/science/article/pii/S0165993615300807#t0010

At first I could not find the safe limits but I found this last night and I was planning to post back here:

https://www.who.int/news-room/fact-sheets/detail/mercury-and-health

Mild, subclinical signs of central nervous system toxicity can be seen in workers exposed to an elemental mercury level in the air of 20 μg/m3 or more for several years. Kidney effects have been reported, ranging from increased protein in the urine to kidney failure

If we assume a sealed room, say 2m x 2m x 2m, and 100 operations of the device, we end up with a worst case final concentration of 2 μg of mercury or 0.25 μg/m3.

So the worst case is nowhere near the threshold of "mild, subclinical toxicity".

 

[russ_watters]

I did find this document where they directly give values for the saturated Hg concentration -- it's about 20 ng / cm^3.
https://www.sciencedirect.com/science/article/pii/S0165993615300807#t0010

At first I could not find the safe limits but I found this last night and I was planning to post back here:

https://www.who.int/news-room/fact-sheets/detail/mercury-and-healthIf we assume a sealed room, say 2m x 2m x 2m, and 100 operations of the device, we end up with a worst case final concentration of 2 μg of mercury or 0.25 μg/m3.

So the worst case is nowhere near the threshold of "mild, subclinical toxicity".

Excellent analysis, thank you! So few people actually do the simple calc.

It's worth noting that your calculations are very conservative; no ventilation and 100 tests is a stagnant room and an arm that's numb from lack of blood flow.

 

[Swamp Thing]

Thanks for the comment and the like.

an arm that's numb from lack of blood flow

Well, there could be a few people in there testing each other in turn.

But then, they would be sharing the mercury vapor, which would reduce individual exposure even further

 

[Tom.G]

If we assume a sealed room, say 2m x 2m x 2m

Well, there could be a few people in there testing each other in turn.

Until they die of hypoxia.

On the average, an adult at rest consumes about 16 liters of oxygen per hour.
(from: http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/metab.html)

Hmm... Maybe not so bad, 4 people could remain conscious for (very) roughly 30hrs.

Cheers,
Tom