"If there's a hole in a sodium hypochlorite truck, the liquid spills on the ground and there's no big toxic cloud. It's what they call an inherently safe technology."
I read this in an article recently published by The Times-Picayune about the New Orleans Sewerage and Water Board’s plan to switch from using chlorine gas to sodium hypochlorite as its primary disinfectant. The goal is to reduce the risk of a catastrophic chlorine gas leak in neighborhoods surrounding the plant due to either railroad tankcar accidents or terrorist acts.
Risk reduction, especially for densely populated areas, is a smart move.
But statements like this about sodium hypochlorite, commonly referred to as bleach, just make me cringe.
False sense of security surrounding bleach
I feel uneasy because customers have told me that bleach is safe. I’ve read proclamations that the risk of a chlorine gas leak has been eliminated by switching from chlorine gas to bleach.
It’s not. And it hasn’t.
Bleach contains chlorine, treat it with the respect you give chlorine gas
This isn’t about bashing sodium hypochlorite; we need it to keep our water safe to drink. The point is it contains chlorine and needs to be treated with the respect it deserves; the same respect which is given to elemental chlorine gas.
The statistics don’t lie; you still need a gas detector
Given the number of reported incidents of chlorine gas exposure caused by accidentally mixing sodium hypochlorite and acid, we always recommend that a bleach storage area should include a chlorine gas leak detector. It not only helps protect personnel and equipment, it can also help demonstrate that everything possible was done to limit the consequences of an accident.
Sodium hypochlorite can produce the same chlorine gas that's being eliminated
Sodium hypochlorite’s properties and characteristics require careful consideration to ensure disinfection of the process water and safe usage through proper equipment selection, maintenance, and handling.
- Sodium hypochlorite degrades over time, which reduces the amount of available chlorine for disinfection and produces undesirable byproducts.
- Combining bleach with acids can release elemental chlorine gas, the same stuff that’s being eliminated by many treatment plants.
- Sodium hypochlorite can be explosive if mixed with many organic compounds, including petroleum products such as oils, fuels and grease. Other toxic and flammable gases can be generated by improper mixing with other chemicals under certain conditions.
- Under certain conditions, sodium hypochlorite that has dried on rags or clothes can spontaneously combust. Higher concentrations that dry in heated conditions, such as around pump seals, can become ignitable or explosive on impact.1
There are numerous other hazards that users need to consider for safe operation. The Chlorine Institute has a wealth of knowledge regarding chlorine and sodium hypochlorite, including free brochures available for download. If you use bleach, we urge you to check it out here.
A switch from chlorine gas to bleach can reduce the magnitude of a chlorine gas leak. At the same time it switches the type of risks, which requires care to ensure the liquid is used as safely as possible.
I look forward to hearing your view on the subject.
1. White’s Handbook of Chlorination and Alternative Disinfectants, 5th Edition, Black & Vetch Corporation, Hoboken NJ: John Wiley & Sons, Inc. 2010, P 463