Pool training is essential for developing safe diving skills, and training facilities need to balance many factors including safety, maintenance, and environmental considerations. Recently, I've been researching how different weight systems affect pool facilities, particularly regarding water quality. My background is as a chemical engineer with quite a bit of experience in water chemistry, so I thought I’d do some research and estimates.
Understanding Lead in Diving
Lead has a long history in diving because it is stable in water, dense, and relatively cheap. While metallic lead is fairly safe, dissolved lead poses a significant problem. Living in Michigan, the Flint water crisis has made us acutely aware of lead's risks in water systems.
The Pool Environment Challenge
In open water, any lead released from weights gets diluted by massive water volume. Swimming pools present a different scenario - the water is recycled and shared between divers and recreational swimmers, including children. While pool chemistry is carefully controlled for many parameters, lead concentration typically isn't one of them.
Practical Solutions for Divers
If you're concerned about lead weights in swimming pools, here are some practical approaches:
I've experimented with several stainless and tungsten shot alternatives. In all cases, I’ve put them in new velcro mesh bags that can be purchased as replacements for lead shot bags. Examples are from XS scuba. There are many suppliers of these—check around for the best prices.
Stainless Steel Fill
I’ve made some of my own stainless shot weights using tumbling media and stainless shot blasting material.
The tumbling media I’ve used is from BC Precision 1/8" 304 Stainless Steel Ballcone Tumbling Media.
Cost: $20/lb if you buy small quantities or $6.40 lb if you buy 100+ lbs. Shipping adds some but it isn’t crazy.
Stainless steel shot blasting media also works.
Cost: $4.75/lb for small quantities and $4/lb for larger. Note shipping prices are expensive from them, so if you can pick them up yourself in Cleveland OH if you are near enough.
Tungsten Fill:
I’ve made weights with tungsten shot: size 1 buck to minimize surface area.
Cost: $52/lb + shipping.
This can get expensive, but tungsten is more dense than lead (19.3 g/cm3 vs 11.34 g/cm3). The tungsten shot weights should have a volumetric density of about 12.5 g/cm3, so greater than that of a solid lead block.
Note that while tungsten is very stable in water, there are some reports of tungsten rings tarnishing in swimming pools. This and the health impact of tungsten in water is not well studied, mostly because tungsten contamination is rare. Caveat emptor.
TECHNICAL ANALYSIS
For those of you who are curious, below is a conservative analysis of potential lead release from dive weights. These calculations use the lowest documented lead corrosion rate to establish a minimum baseline.
—
Lead corrosion rate: 0.002 mm/year
This is the lowest observed corrosion rate for lead I’ve read and about that of stainless steel. This particular estimate is from Gatun Lake in Panama in fresh water in Table 2 of this paper.
I note that in this same report they see higher rates of up to 0.015 mm/year. And this assumes no abrasion or disturbance of the lead surface—something unlikely for a dive weight.
Translating this 0.002 mm/year corrosion rate to a leaching value we have 2.6x10^-4 mg/(cm2-hr)
—
Solid dive weight surface area: 71 cm2/lb
This is based on a CAD drawing of a 1.5 kg lace through dive weight mold.
—
Shot weight surface area: 1200 cm2/lb
This assumes a 2 mm spherical lead shot. Surface area is likely greater as the shot is not actually spherical, but this is a base case.
—
Typical dive class: 8 people in the water (includes instructors), 2 hours long. Each person has an average of 15 lbs of weight on them.
For this class, we would have 120 lb of lead in the pool for 2 hours for the class. Assuming our leaching values:
All solid weights: 4.4 mg/class
All shot weights: 74.56 mg/class
—
In a typical pool of 100,000 gallons this translates to a change in lead concentration of:
All solid weights: +0.01 ppb
All shot weights: +0.2 ppb
Not a lot, if we take the WHO lead action level of 10 ppb for drinking water as standard, with a goal of 0 ppb of lead, then any additional lead burden is not desirable.
—
But classes don’t just happen once and pool water is not constantly refreshed. Assuming an average pool fresh water addition rate of 3% per week (typical for a normal municipal swimming pool) and 5 scuba classes per week, the steady state lead concentration from dive weights alone is:
All sold weights: 1.93 ppb (below action level)
All shot weights: 33 ppb (above action level)
This approximation makes many assumptions, central to them is the absolute lowest corrosion rate of lead that I could find. It would not surprise me if the actual corrosion rate in the pool were 5x or more due to chemistry and agitation, but I’ve found no data to help clarify that for me.
Pool Chemistry Considerations
The interaction between lead and pool chemistry is complicated and I don't have good data here. Some might assume that pool chlorine protects lead weights by forming a protective coating, similar to how salt water can create protective lead chloride layers. However, pool chemistry works differently. Swimming pools use free chlorine (HOCl and OCl-) as an oxidizing sanitizer, which is chemically distinct from the chloride ions (Cl-) found in seawater. This free chlorine can actually promote lead corrosion rather than prevent it.
In salt water pools, the situation becomes more complex with both chloride ions and electrolytically-generated free chlorine present. While chloride ions might form protective layers, constant weight handling would disrupt this protection. The oxidizing environment, pH adjustments, and shock treatments further contribute to potential lead release.
Practical Implications
Pool operators face trade-offs with different weight types. Shot weights reduce impact damage but create cleanup challenges if spilled. Uncoated lead weights can mark pool surfaces, and these marks represent additional lead sources in the water system.
While most pools don't monitor lead levels, these conservative calculations suggest that lead exposure could be significant, particularly with lead shot weights and high pool usage. As divers, we should consider how to minimize this risk for ourselves and others sharing these facilities.
I'm interested in hearing others' experiences with non-lead shot weights. What alternatives have you tried?
Understanding Lead in Diving
Lead has a long history in diving because it is stable in water, dense, and relatively cheap. While metallic lead is fairly safe, dissolved lead poses a significant problem. Living in Michigan, the Flint water crisis has made us acutely aware of lead's risks in water systems.
The Pool Environment Challenge
In open water, any lead released from weights gets diluted by massive water volume. Swimming pools present a different scenario - the water is recycled and shared between divers and recreational swimmers, including children. While pool chemistry is carefully controlled for many parameters, lead concentration typically isn't one of them.
Practical Solutions for Divers
If you're concerned about lead weights in swimming pools, here are some practical approaches:
- Avoid shot lead in pools. The high surface area of shot leads to the greatest potential lead release.
- Use coated solid weights if using lead. A good coating prevents lead leaching and protects pool surfaces. These are widely available and only slightly more expensive than uncoated weights.
- Make your own non-lead shot alternatives. While more expensive, stainless or tungsten shot in replacement weight bags offers a lead-free solution.
I've experimented with several stainless and tungsten shot alternatives. In all cases, I’ve put them in new velcro mesh bags that can be purchased as replacements for lead shot bags. Examples are from XS scuba. There are many suppliers of these—check around for the best prices.
Stainless Steel Fill
I’ve made some of my own stainless shot weights using tumbling media and stainless shot blasting material.
The tumbling media I’ve used is from BC Precision 1/8" 304 Stainless Steel Ballcone Tumbling Media.
Cost: $20/lb if you buy small quantities or $6.40 lb if you buy 100+ lbs. Shipping adds some but it isn’t crazy.
Stainless steel shot blasting media also works.
Cost: $4.75/lb for small quantities and $4/lb for larger. Note shipping prices are expensive from them, so if you can pick them up yourself in Cleveland OH if you are near enough.
Tungsten Fill:
I’ve made weights with tungsten shot: size 1 buck to minimize surface area.
Cost: $52/lb + shipping.
This can get expensive, but tungsten is more dense than lead (19.3 g/cm3 vs 11.34 g/cm3). The tungsten shot weights should have a volumetric density of about 12.5 g/cm3, so greater than that of a solid lead block.
Note that while tungsten is very stable in water, there are some reports of tungsten rings tarnishing in swimming pools. This and the health impact of tungsten in water is not well studied, mostly because tungsten contamination is rare. Caveat emptor.
TECHNICAL ANALYSIS
For those of you who are curious, below is a conservative analysis of potential lead release from dive weights. These calculations use the lowest documented lead corrosion rate to establish a minimum baseline.
—
Lead corrosion rate: 0.002 mm/year
This is the lowest observed corrosion rate for lead I’ve read and about that of stainless steel. This particular estimate is from Gatun Lake in Panama in fresh water in Table 2 of this paper.
I note that in this same report they see higher rates of up to 0.015 mm/year. And this assumes no abrasion or disturbance of the lead surface—something unlikely for a dive weight.
Translating this 0.002 mm/year corrosion rate to a leaching value we have 2.6x10^-4 mg/(cm2-hr)
—
Solid dive weight surface area: 71 cm2/lb
This is based on a CAD drawing of a 1.5 kg lace through dive weight mold.
—
Shot weight surface area: 1200 cm2/lb
This assumes a 2 mm spherical lead shot. Surface area is likely greater as the shot is not actually spherical, but this is a base case.
—
Typical dive class: 8 people in the water (includes instructors), 2 hours long. Each person has an average of 15 lbs of weight on them.
For this class, we would have 120 lb of lead in the pool for 2 hours for the class. Assuming our leaching values:
All solid weights: 4.4 mg/class
All shot weights: 74.56 mg/class
—
In a typical pool of 100,000 gallons this translates to a change in lead concentration of:
All solid weights: +0.01 ppb
All shot weights: +0.2 ppb
Not a lot, if we take the WHO lead action level of 10 ppb for drinking water as standard, with a goal of 0 ppb of lead, then any additional lead burden is not desirable.
—
But classes don’t just happen once and pool water is not constantly refreshed. Assuming an average pool fresh water addition rate of 3% per week (typical for a normal municipal swimming pool) and 5 scuba classes per week, the steady state lead concentration from dive weights alone is:
All sold weights: 1.93 ppb (below action level)
All shot weights: 33 ppb (above action level)
This approximation makes many assumptions, central to them is the absolute lowest corrosion rate of lead that I could find. It would not surprise me if the actual corrosion rate in the pool were 5x or more due to chemistry and agitation, but I’ve found no data to help clarify that for me.
Pool Chemistry Considerations
The interaction between lead and pool chemistry is complicated and I don't have good data here. Some might assume that pool chlorine protects lead weights by forming a protective coating, similar to how salt water can create protective lead chloride layers. However, pool chemistry works differently. Swimming pools use free chlorine (HOCl and OCl-) as an oxidizing sanitizer, which is chemically distinct from the chloride ions (Cl-) found in seawater. This free chlorine can actually promote lead corrosion rather than prevent it.
In salt water pools, the situation becomes more complex with both chloride ions and electrolytically-generated free chlorine present. While chloride ions might form protective layers, constant weight handling would disrupt this protection. The oxidizing environment, pH adjustments, and shock treatments further contribute to potential lead release.
Practical Implications
Pool operators face trade-offs with different weight types. Shot weights reduce impact damage but create cleanup challenges if spilled. Uncoated lead weights can mark pool surfaces, and these marks represent additional lead sources in the water system.
While most pools don't monitor lead levels, these conservative calculations suggest that lead exposure could be significant, particularly with lead shot weights and high pool usage. As divers, we should consider how to minimize this risk for ourselves and others sharing these facilities.
I'm interested in hearing others' experiences with non-lead shot weights. What alternatives have you tried?