Does chlorine freeze? Everything commercial pool operators need to know

Do you feel that? It’s the icy winds of winter arriving to stay for awhile and whether you operate aquatic facilities indoors throughout the winter and spring or not, it’s important to understand where you can store your pool chemicals throughout the cold temperatures. Ahead, we’ll address the common question, does chlorine freeze, as well as cover some general tips for safe winter pool chemical storage. 

Does chlorine freeze?

Known for its “strong oxidizing capabilities” that enable it to disinfect, chlorine is a highly reactive hydrogen element that easily forms compounds with several other elements, including sodium and hydrogen. In other words, while you want chlorine to form hypochlorous acid, the compound that sanitizes and disinfects water, it’s also important to handle it carefully and store it safely, keeping it separate from chemicals you don’t want it reacting with.

One of its pool chemical forms is also one of the most widely used ones, sodium hypochlorite or liquid chlorine, which is commonly used as a pool shock. This is the form you most need to worry about freezing. 

Liquid chlorine can freeze, though the good news is, it freezes at a lower temperature than water. While water freezes at 32℉ (0℃), liquid chlorine freezes at approximately 19℉ (-7℃), with slight variations depending on the concentration of sodium hypochlorite in the solution you’re storing. 

Unfortunately, when liquid chlorine freezes, the process causes the chemical to separate, decreasing its effectiveness. While it will thaw, it won’t be as effective a sanitizer in pool water. So whether you’re relying on it throughout winter operations, or reaching for it again once the pool reopens, it’s important to store it properly and protect it from freezing. 

How to store liquid chlorine (and all pool chemicals) in the winter

These pool chemical storage tips are applicable year-round, but while we’re talking about winter storage, the first thing to ensure is that you’re storing all pool chemicals in cool temperatures where they are protected from extreme temperatures, including freezing temperatures and heat.

As we mentioned, liquid chlorine will freeze and as a result, separate, and so will other liquid chemicals, rendering them unusable. If you store pool chemicals outside during the summertime, bring them to an indoor storage area during the winter. 

Pool chemical storage areas should be:

• Cool and dry, and away from sunlight, moisture, and humidity
• Well ventilated. If storing chemicals inside their own storage cabinet, both the cabinets and the storage area itself should be well-ventilated to prevent fumes from building up
• Designated for pool chemicals only. You should avoid cross-contaminating pool chemicals with other facilities chemicals and substances, including bleach and gasoline.
• Waterproof and free from flooding danger. Water reacts quickly and easily with several chemicals, including stabilized and non-stabilized chlorine, and will cause fires, explosions, and significant health and safety hazards

Other critical tips for pool chemical storage include:

• Always store pool chemicals in their original, manufacturer-issued packaging
• Store chemicals off the ground, but not so high up that employees are at risk for spilling when reaching for them
• Ensure lids remain tightly sealed
• While freezing temperatures can render pool chemicals useless, leading to expensive replacements, heat can create pressure inside chemicals, leading to dangerous conditions. Keep pool chemicals stored at consistent temperatures below 95℉. 
• It’s also important to keep chemicals away from electrical outlets, heat sources, sparks, or open flame. Post signage warning employees not to smoke around chemicals, and include warnings in your regular, ongoing employee training on safe chemical use.   

What to do if liquid chlorine has frozen

In the case that you’re dealing with liquid chlorine that has frozen, there are a few steps you want to take to ensure safe handling. 

First, inspect the containers for cracks. Then, move the frozen chemicals to a warmer area but avoid direct heat sources of any kind, including sunlight. The key is gradual thawing, which will help prevent the chlorine’s containers from cracking and leaking, which can quickly become dangerous.

Do not use hot water or any forceful impact to thaw frozen chlorine. This can cause dangerous chemical reactions. 

Once the chlorine has thawed gradually, inspect the containers again for any cracks or leaks, even small ones. Then, follow the appropriate local steps for safe disposal. Never reuse containers, and don’t combine the unthawed old chlorine with new chlorine. 

There’s a lot to manage when it comes to pool chemicals, from storage to their actual use in pool water. It’s why we built PoolShark H20, to make it easier, less risky, and faster to test and rebalance pool water. By ensuring you use the exact and correct amount of chemicals you need, it helps prevent chemical overuse. Its locked records help you track pool water safety and chemical use, so you can buy less, spend less, and store less chemicals.