Tuesday, January 09, 2007
BOOM GOES THE DYNAMITE
Then I found this in the Department of Health and Community Services Draft Public Health Guidelines for Aquatic Facilities, Norther Territory, Australia:
"4.5 Special Requirements for Electrolytic Salt Chlorinators
As a byproduct of this process is the production of hydrogen gas (which could accumulate in a pressure filter) Electrolytic Salt Chlorinators shall only be installed downstream of pressure filters. Electrolytic Salt Chlorinators shall be electrically linked to the main circulating pump to prevent the chlorinator operating when the main circulating pump is switched off. Where the electrolytic salt cells are not designed to be located above the filter vessel gas detectors shall be fitted that will terminate the operation of the chlorinator in the event of hydrogen gas build up.
As an Electrolytic Salt Chlorinator cannot respond to instantaneous chlorine demand a backup chlorine system shall be installed, using gas, liquid or granular chlorine."
Perhaps David was just talking about his territory when he said that salt systems weren’t authorized on commercial pools. Or perhaps he’s right. This is a Draft plan, so maybe they’re not yet authorized in the Northern Territory. But they must be at least planning to approve them. Otherwise they wouldn’t be going to all the trouble of spelling out how to properly install those salt systems and about using back up gas detectors so they won’t blow up.
You knew that they could blow up, right? I mean, I’m sure your Sales Rep told you that if your salt cell wasn’t properly installed, or if your flow sensor failed to operate correctly and your pump motor went out, or you closed the wrong valve, or your system lost prime, that the cell could keep generating chlorine without water flow, and that after a little while, one of the byproducts of the process, hydrogen gas, could build up in the cell and in the plumbing and reach an explosive level and, well... explode. You know, like BOOM and flying shards of PVC and plastic shrapnel kind of explode. Oh, yeah, and flying titanium plates, too. I forgot about those.
I know. I know. I’m being terribly alarmist. Or am I?
Here’s an inventor named Ben Bremauer who has applied for a patent for his version of a chlorine generator - he calls it an electrolytic sanitiser generator. Ben talks about the shortcomings of the safety devices currently in use to avoid hydrogen gas build up.
"Although an adverse byproduct of this process is the production of hydrogen gas H.sub.2(g), under normal operating conditions the H.sub.2(g) flows with the feed water into the body of water and escapes safely into the atmosphere. However, in some circumstances the water flow conditions may not be normal and it is at these times that safety issues arise with respect to H.sub.2(g) containment. For example, a blocked suction line, closed valve(s), incorrect installation or a seized pump can effect a loss of water flow. It may also cause present safety devices to become ineffective, inoperable and/or redundant. In such circumstances, the cell may continue to produce H.sub.2(g) such that the volume of H.sub.2(g) contained in the system may reach dangerously explosive levels. The H.sub.2(g) may continue to be produced and fill not only the cell chamber but all the filtration system plumbing and receptacles. A large H.sub.2(g) reservoir may result leading to a potentially explosive situation.
 Electrolytic cells have been disclosed in which the electrodes are positioned in between inlet and discharge ports of the cell with no provision to trap and contain hydrogen gas in the event of a water flow stoppage. These cells are plumbed horizontally or vertically and may use flow switches plumbed in series with the cell to detect a water flow fault condition. In such an arrangement, the flow switch may be designed to suspend power to the cell to minimise the potential a H.sub.2(g) build up.
 The use of a flow switch may be considered a good primary safeguard against a loss of water flow. However, the use of a flow switch alone as a single safe guard against hydrogen gas build up has been found, in the inventor's experience, to be insufficient. A flow switch is a mechanical device and therefore has a potential for failure. In the event of a water flow stoppage, a flow switch failure could cause a massive hydrogen gas volume to accumulate in the plumbing and filtration equipment and therefore become hazardous. To the inventor's knowledge and belief, this one safety device, which the inventor believes should only be used as a primary measure, is the only safety feature relied upon by electrolytic chlorinators currently on the market." (Emphasis mine)
Now, full disclosure here requires me to tell you that installation guidelines for salt systems has the installer using the load side of your filter pump timer, so that when power to your pump is interrupted, power to your salt system is interrupted as well. But it doesn’t take into account, nor can it, the failure of your salt system’s only safety feature, the flow switch, and then a misalignment of your valves (Gee, no one ever does that!), or a failure of your filter pump motor, or a blockage of your system that causes it to lose prime (like a low water level at your skimmer). Any of these things combined with a faulty flow switch could allow your salt cell to keep running and through the process of electrolysis, continue to produce chlorine and all of it’s byproducts, one of which is highly explosive hydrogen gas.
You know. Hydrogen gas. Of Hindenberg fame? "Oh, the humanity!" You remember, right?
Ben goes on to point out the two types of flow switches that are currently in use:
" Cells have been disclosed having separate flow switches or integral flow switches which operate at 90 degrees to the direction of flow. A cell may be installed without plumbing the cell in a gas loop and where the cell is at the uppermost portion of the loop. In such an installation, an integral flow switch or a separate flow switch may be installed but a failure of the flow switch to detect a water flow failure could lead to a hydrogen gas build up.
 Other manufacturers have used a non mechanical conductive electrode arrangement positioned at the top of a horizontal cell chamber. However, such methods detect only the presence of water and not the flow of water. It may therefore fail to detect a lack of flow of water if the cell is not installed in the horizontal position as generally specified in installation instructions. Moreover, incorrect installation may find the sensor positioned at the lower portion of the cell rendering it effectively redundant. Incorrect orientation of the cell chamber may cause the inherent physical gas loop to no longer contain hydrogen gas in the event of a flow fault. If both return and suction line valves are closed, the chlorinator cell will continue to operate. The inability of the hydrogen gas to displace the water in the cell may lead to a pressure increase in the plumbing system and eventually damage the plumbing and potentially cause injury."
Now, I’ve had experience with that second type of flow switch. A couple of years ago, I took over a pool and found a salt system installed funny. So, I called the 1-800 tech and ran the installation past him. It was plumbed with the cell on the pool return and wired to go on and off with the main pump. But it was a pool/spa combo, so when you put the valves in the spa mode, you still had power to the salt cell, even though there was no water flowing down the pool return. The 1-800 guy said, "no problem, when you don't have pressure on the pool side, the cell will drain down and sense the loss of water and shut off. That's our way of sensing flow." I told him that when I rotated the valves, that for whatever reason the cell didn't drain down, and he said, "Ooh, that's not good. The thing could build up hydrogen gas and blow up if they run it long enough like that", which I thought was good to know. He recommended that I replumb the system so that the cell was in the common line for both the pool and the spa. But when I told the folks who owned the pool why I wanted to replumb it, that if I didn’t, it might explode, they looked at each other, frowned and then told me to "take the damn thing off" their pool.
This isn’t the first time around for exploding chlorine generators, either. There’s an old system out there, maybe still being used in a few back yards, that uses a brine tank and two chambers to create chorine gas out of salt. In the old systems, when they didn’t get proper attention, sometimes the hydrogen gas vent in the cathode chamber would get clogged. Then, the hydrogen gas would build up and eventually go BOOM. The extra down side of that type system was that it collected the caustic sodium hydroxide in the cathode chamber, as well. So, if it blew up, it spewed caustic liquid all over the place in addition to blowing plastic shrapnel all over everywhere.
But like I said, I’m sure I’m being an alarmist. If there was any real risk that your salt system might blow up, I’m sure there would be huge caution labels all over the unit and in the owner’s manual.
And there are quite a few in the Owner’s Manual, under Installation Instructions. Well, sort of. Some of the manufacturers are better at owning up to it than others. Like Jandy and Pentair do a pretty god job, with big bold Warnings in the Warnings section and throughout the manual’s installation instructions. The next closest is Zodiac, who talks briefly about the possibility of "having a gas build up" and about "possible cell damage". They never use the term flammable gas. Not even once. Which is odd, because they now own Jandy. Makes you wonder, with this new marriage of companies, will Jandy’s tech department rub off on Zodiac and get them to address the issue more forthrightly? Or will Zodiac’s marketing team get Jandy to throttle back on those sales-killing terms like WARNING and FLAMMABLE GAS.
Goldline is the least specific in their installation instructions. The closest they get is:
"Wire the Aqua Rite to the LOAD SIDE of the filter pump timer. It is very important that the Aqua Rite is powered only when the pump is running."
I searched their document for hydrogen, gas, buildup (which returned an excerpt about calcium buildup), and flammable. They’re not there. Look for yourself:
Now, ask yourself this; how many pool owners read the Installation Instructions? If that’s the only place it’s talked about, then it’s not talked about enough. Well, until now, that is.
There are some other references you may want to look at to assure yourself that I’m not just making this issue up. Here are some links to some salt industry pages, geared more for the tech geeks, that talk about the possibility and likelihood of hydrogen gas buildup in salt systems:
http://www.watermaid.co.za/howitworks.htm Read the power supply description.
http://www.salchlor.com/process/process_04.htm This one gives the ratios at which hydrogen gas is safe, flammable, or explosive.
I already know that some sharp Sales Rep out there is preparing his comeback for you on the off chance that you’ve read this and you pose the question "what about the hydrogen gas?". He’ll most likely explain that, hey it’s no different than the people you hear about who mix Cal Hypo with Tri Chlor tabs and get an explosion.
And while that’s true, the difference is, with the Cal Hypo and Tri Chlor, you have to be stupid enough to stand there and mix them and watch them begin to bubble and stick around to see what happens next. With hydrogen gas buildup in a salt system, all you have to do is own a salt system and be the unlucky one that it happens to.
Labels: Exploding Salt Cells