Sunday, November 7, 2010

Death hides in the bilge

Walking down the long dock to my clients boat, I kept getting whiffs of sewer gas, and I thought to myself, someone's boat needs to see the doctor. I step aboard the clients boat, open the sliding glass door to the main salon, and the stench bowled me over. My first thought was the holding tank had to have exploded, or at least sprung a bad leak. I turned on the air conditioning systems, and suspecting that maybe water had evaporated out of an S-trap, or loop, I flushed the heads, and let some water stand in them, ran sink taps, and showers, and then the odor then seemed to dissipate. I opened the hatch to the engine compartment, climbed in and, checked the holding tank, and the lower portions of the bilge, but the whole area appeared to have less odor than the the main salon initially did. At this point, I had already made several errors, but  I never realized it. I called the owner, and told him about the problem, and the owner contacted the maintenance company. A tech came out, and he had seen this problem before, and recognized the odor as hydrogen sulphide gas. 

This boat is very well maintained. I take care of the electronics, and another firm does everything else. The boat had been checked a week earlier, and the batteries had been checked for water levels. This is a 24 volt boat, with two banks of four batteries each, and you can see one of the batteries above, with a now swollen case. There is a high quality charger on board, and only the starter battery bank, has a temperature sensor. Somehow, in a very short period of time, four identical batteries in the house battery bank, nearly boiled dry, and the side effects of this, are what this story is all about.

The lead acid batteries used in our boats, are a far cry from the one invented by Gaston Plante in 1859. Like most of us, I know there are lead plates, submerged in an electrolyte (sulphuric acid and water), that undergo some electrochemical reaction to create Mr. Electricity, and that is about where my real understanding stopped, until recently. Batteries have come a long way from Mr. Plante's simple roll of lead separated by linen cloth, and immersed in sulphuric acid. Todays batteries are sophisticated structures, and are made of a complex mixture of metals, and chemicals.

The primary ingredients we are going to learn about, are hydrogen, sulfur, oxygen, and antimony. Your battery, in its normal course of activities, creates both hydrogen, and oxygen while charging, and these are reabsorbed during the discharge cycle. It's when things become abnormal in your battery, that bad things can happen. If the electrolyte (water and sulphuric acid) levels drop in the battery, exposing the plates, sulfates that are now exposed on the lead plates, start to combine with the hydrogen gas created during charging, and hydrogen sulphide gas is created.

Two other gases can form, depending on the construction of the batteries. Lead by itself, is not a very strong material, and is generally alloyed with the element antimony to make the lead stronger. Another item, that can be present, in the lead plate's alloy mixture, is arsenic. So again, if the plates become exposed, the hydrogen gas atoms will also combine with antimony atoms, to make Stibine gas. And if arsenic is present in the alloy mix, Arsine gas can be created. Both of these are even more toxic than hydrogen sulphide gas, and also very flammable.

Hydrogen sulphide gas, sometimes called sewer gas, or rotten egg gas, does occur naturally, and is created by decomposing organic material. It does smell very much like the inside of your holding tank. So while I was running around inside the boat, thinking something was awry with the holding tank system, what I was really smelling, was hydrogen sulphide gas, and this is a dangerous, and toxic material. It is very flammable, heavier than air, and very poisonous. At low concentrations, you can smell it, but at slightly higher concentrations, around 100 ppm, it paralyzes the olfactory nerve, and the odor goes away. So when I went down into the engine compartment, and It didn't seem to have any notable, odor, my smeller had been shut down by the gas. At between 300 to 500 ppm, death is a possibility, and at 1000 ppm death is almost immediate.

I did a lot of digging around, and cases of pleasure boaters who have died from breathing hydrogen sulphide are rare. Less rare are explosions on boats initiated by hydrogen gas/hydrogen sulphide gas coming from batteries. In the end, your boat batteries are both a blessing, and if not properly cared for, a curse.

In this case, I am not sure what happened, other than somehow the four large flooded lead acid batteries, in one of two battery banks, in a very short period of time, had the majority of the electrolyte boiled out of them. This created a very dangerous situation, either from explosion, or breathing the associated gases. New batteries were installed, and everything now appears normal. But the reason the problem occurred in the first case, needs to be found. Charger problem? Installation problem? Alternator problem? Shorted battery?

The typical gas sensors on a boat are not designed to sense these gases, so no warning was available, other than the very strong odor, which goes away with exposure. I have to be honest, I was a more than a little startled about both my specific lack of knowledge, and my potential exposure to the gas.

I will do my best to discover the cause of the problem. It had to have had a source, and I will do a second story soon, when I find out what actually did happen, and learn even more. I will also include some do's, and don'ts when dealing with your batteries, and some thoughts about battery types to use.  I am a lot smarter now, and I hope to get even smarter.

If you have had any personal experiences with hydrogen sulphide gas, and or battery related explosions, I would like to hear about it. You can use the comment, or the email links below. Thank you, Bill

I have a few links below to review.
Case report of a marine technician killed by an exploding battery
Hydrogen Sulphide in low maintenance batteries

The diagram of the battery is from the The Association of European Automotive and Industrial Battery Manufacturers website


  1. Bill, check the temp sensor read out on the charge controller. In August, ours failed. Its signal went to 1/100th of what it should have been -- a 90 deg battery showed as a 0.9 deg battery. The temperature compensation firmwware in the charger adjusted the bulk, accept, and float voltages to levels appropriate to those temperatures. Those voltages were essentially "equalize" voltages for the AGM batteries. The charger pumped 436 AH into the bank until the battery physically closest (not electrically, they are in parallel) to the charger shorted out. By this time it had boiled and spewed liquid from the vent. The H2S produced caused all wiring insulation in the boat to turn varying shades of brown -- looms accelerated the flow of the gas into remote spaces. The two remaining 5 yr old batteries survived a subsequent 20hr test at about 10% reduction in expected capacity. So the whole bank is being replaced next month. A new charger temp sensor will not be used until I can add a voltage sensing relay to protect against over-voltage in case of another failure. In the mean time, I am using the solar panels in lieu of the charger to keep the batteries topped. The controller for them has a temp sensor as well, but it has built in selectable voltage limits. Temp sensors seem to be of use mainly in dealing with battery compartment temp fluctuations from engine use. Temp control for water temp fluctuations or weather is pretty easy to stay on top of manually.

  2. I think that Chris is on to something in suspecting an errant temperature sensor. When troubleshooting inverter/chargers, chargers or external alternator regulator issues, the tech manual (or tech support) will always have the temperature sensor disconnected from the equipment to ensure it is not causing the problem.

    I have personally had two temperature sensors fail on clients' vessels.


  3. Thanks Charlie, and Chris, I will give these sensors a very solid scrub. Tnx Bill

  4. Not only is it poisonous and smells really bad but the gas emitted is explosive as well. I've been in one battery room fire (100+ lead acid batteries) and, in most ship fires you need to secure ventilation but that is the wrong move... you need to 1) get any people out then 2) the gas out before you go in and try to extinguish the fire.

  5. Thanks for the comment John, this was only four batteries a boiling, I can't imagine 100+ batteries, and on fire. I am writing a follow up story. Bill

  6. I do not have this kind of experience my battery are charge by solar panels and Balmar charge controller for the alternator the battery are located under a bunk and i will like to install a forced ventilation with a square ventilator 12V computer like i wish to overate this ventilator only when the battery reach 13.5v or more if some whone have any suggestions ow to complete this installation the recommendations will be appreciated.

  7. I found this write up of yours as a result of finally figuring out what was wrong with me, it wasn't a common cold as I felt a bit different; "chemical pneumonia" cost me a week of work. I was in the engine room almost an hour before my work brought me to the battery banks (the impeller overhaul job was on the AQ151c's were via the cabin access). One battery had exploded and was ruptured, missing it's fluid fill cap, charging cables laying near by. A nearby battery looked just as bad inside and was leaking between cells. I thought the owner took off the water caps but his cheap only-15-amp charger cooked his batteries between his visits, filled the engine bay with hydrogen sulfide gas. Although both engine accessory bay doors were open during the 4 hours there, it's been a week and I only just now am feeling better but missing thanksgiving dinner this evening. I have found that Hydrogen Sulfide detectors are about $100+ and good for 2 yrs, same price for oxygen detectors from same company. I couldn't smell anything, and foolishly believed I'd be able to smell anything "unbreathable". I have an achy cough and endured an odd chemical sensation that kept me unmotivated and dull. This has happened before, certainly as a result of other boat batteries like the one (I lived aboard for a few months) but as I write this I'm feeling better and better and suspect that tomorrow I'll be shocked at the unproductive previous week. I have good clients that are happy to have me aboard, having only gone full time in the last 4 months, I'm grateful of this learning experience (surprised worse hasn't happened to me sooner) and will be ordering wearable detectors tonight.

    1. Vince, thanks for that sobering story, and I'm glad you're feeling better and the effects weren't permanent. I was very startled myself and I'm ultra conscious now to look look for the gas. As I mentioned it takes your smeller out quickly at higher concentrations. That's why I thought everything in the engine room OK when in fact it wasn't at all. I was lucky, and now much smarter. Bill

  8. This is interesting. We live in Alaska, and the last four times we have gone out on my hubby's 70' Symbol (2001 model), my lips have swollen up (and one time the inside of my mouth) after being on the boat for about 12 hours. He did a lot of checking for different things, finally borrowed a sensor from a shipyard. The sensor indicated dangerous levels of gases in the engine room. He looked at the water in the batteries and realized one was nearly empty. I think this is the problem. My lips were the 'canary in the coal mine' so to speak. Maybe we are onto the problem. Scary.

  9. Farrell, glad you found the source, and it is scary. After a couple of minutes you can't smell it. Some of the other symptoms are numb feet and hands, wheezing, burning pain, memory problems, nose bleeds and yes swollen lips and mouth although this last one is most often noticed post mortem.