Lye explosion - Help!

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I’ve been making soap for 5 years now and have a small soap making business. Today I was making a batch of laundry soap which I’ve been making for years with no problem. I disolved my citric acid into my distilled water and then added the lye add it exploded, got on my shirt and now I’ve got 2nd degree burns on my stomach (not that bad). I’ve never had this happen before. Can anyone think of what I could have done wrong so it won’t happen again?
 
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I disolved my citric acid into my distilled water and then added the lye add it exploded, got on my shirt and now I’ve got 2nd degree burns on my stomach (not not that bad).

Glad to hear the burns aren't bad. While I don't wear long sleeves, long pants or shoes, or gloves...I do wear a 'slick' apron.

So...process of elimination: New CA supplier? New NaOH supplier? What was the temperature of the water? How large was the amount of NaOH used? Did you pour it in or did you dump it in?
 
Good idea about the apron, I think I’ll use one next time. Lucky I always soapin shirts I don’t care about just in case.

It was a laundry bar so it’s pretty lye heavy but I’ve never had issues with it before. I’m always careful about slowly pouring the lye in. The only thing I can think of is maybe the water was too hot, I usually heat it in the microwave to dissolve the citric acid and then let it sit and cool down before I add the lye but I don’t usually check the temperature, maybe it was too hot? I was a little distracted, my baby learned to crawl this week so I got to keep half an eye on him. Do you know the optimum temperature for the water should be before you add the lye?

My lye is the same brand as I always use but it was the very last of the jar, could I have gotten it contaminated in some way? I soap at least once a week and have been busy making bars for the holidays and maybe I didn’t put the cap back on? I’ve been master batching lye water this week so I’ve had the jar out more than usual.
 
Dissolving NaOH in water is bad enough, but dissolving NaOH in acids (citric acid, lactic acid, vinegar, lemon juice) is much worse! You have to add the lye in many small steps, and wait in between until it has cooled down again. Had lemon juice in a cold water bath boiling.

The lye+water gives off heat two times: first during dissolving (saturated solution), and once again when the concentrated solution is diluted with the rest of the water (streaks rising from the dissolving lye beads). With lye masterbatching, you can defer the dissolution heating to another day, but the dilution heating is still there.
With acid, you have a third kind of heating: neutralisation (acid + lye → salt + water + heat). When all three heat sources come together, the result can be catastrophic, just as you have experienced.

@TheGecko is right that you should think about what has changed (also including stupid errors like weighed too much citric acid). But less so why this reaction now has occured (it is absolutely normal that lye behaves this way), but why it hasn't done so before (Old lye deactivated by air contact? Colder batch water?).

An obvious recommendation would be lye masterbatching, i. e. prepare a large amount of 50% NaOH in water solution beforehand, and store/use it at room temperature. That way, you save yourself from the dissolution heat. Or use (tri)sodium citrate instead of citric acid, which avoids the neutralisation heat.


ETA: Just saw that you replied. Don't use the microwave to dissolve the citric acid. It will do so all by itself (or you might prepare a 50% solution of it beforehand). If you're impatient, you could add a tiny bit of NaOH into the citric acid (with heavy stirring), so that the neutralisation heat plays the role that would have had the microwave.
 
Thank you! I didn’t know that about the citric acid, funny I’ve made a fair amount of vinegar hardened bars and never had a problem. Maybe citric acid is more reactive? I’ve not actually made that many bars with it. I don’t normally chelate my soaps, I only do it with my laundry bars because I don’t want soap scum in my washing machine. I usually only do one batch of laundry soap a year but with the baby I’ve had to do so much more laundry I’ve had to make more. Thank you for the tip about not needing heat to dissolve the citric acid, I’m so used to doing that with salt and sugar I just assumed it needed it also.

I just retried my laundry soap recipe again and it worked fine. Now I’m wondering if I incorrectly measured my citric acid. Thank you so much!
 
So sorry to hear of your injury, and so glad it wasn't worse. I would agree with RO that the combination of CA + heat + lye was the cause of your incident.

The only lye explosion I've ever had was when I absent-mindedly dumped all of the batch lye into the vinegar I was using as a 100% water replacement. It didn't actually blow up, but it was definitely an overflowing volcano of bubbling caustic liquid. Never again!

EDITED; I always laugh when I see recommendations to use boiling water to dissolve citric acid. Even just a smidge of warmth to the liquid is enough to help citric acid, sugar and salt dissolve more easily. But as noted, you can use room temp water; it will just take a bit longer.
 
Thank you for the tip about not needing heat to dissolve the citric acid, I’m so used to doing that with salt and sugar I just assumed it needed it also.

I have never heated my water for salt and sugar, either. I find they both dissolve pretty easily in water.
 
Makes me glad I got sodium citrate. This is a good reason to always always always wear safety glasses.

Regarding citric acid, it's cheap and easy to use once you have got the process down, but comes with a few extra complications that other additives don't bring. The mixing as you found out is dicey, but it's not just the reaction, it's also the accuracy I have issue with. Apparently SMFcalc does not give the correct amount of NaOH that will be neutralized per gram CA added (.46 grams vs DeeAnna's recommended .624 grams). So we have to do side calcs in addition to using the soap calc.
 
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