Chlorine Gas in Pools: All You Need to Know

Gas Chlorine is an unstabilized, inorganic compound that exists in a gaseous state. It has 100% available chlorine and the same percentage of active strength. In a 1% solution, it lowers the pH to 0.  Chlorine gas is a greenish-yellow gas that is 2.5 times heavier than air. It is used in various industries, including the pool industry where it is referred to as gas chlorine. It is also known as “liquid chlorine” or “liquefied chlorine gas” outside the pool industry. Chlorine gas is hazardous and can cause irritation to the eyes, nose, and throat. It can be lethal in extreme cases. Despite its dangers, it is popular due to its cost-effectiveness. It is also highly soluble in water and is primarily produced using electrolytic cells.

What are the Characteristics of Chlorine Gas?

Chlorine gas is two and a half times heavier than air and light green in color. It lowers the pH of water when introduced and is 100% available. However, it’s difficult to handle and potentially lethal. It can cause severe eye, nose, and throat irritation and in extreme cases, it can be lethal. It is also highly soluble in water.

How is Chlorine Gas Produced?

Chlorine gas is primarily produced using three types of electrolytic cells: diaphragm, mercury, and membrane. It is typically made from a solution of salt (brine), water, and electricity. In the US, about 70 percent of chlorine gas is produced by the diaphragm cell, totaling approximately 11.6 million tons or 2.3 billion pounds annually.

How much Chlorine is in Chlorine Gas?

Chlorine gas is pure, with a chlorine weight in the formula (Cl) of 100%.

What is the Solubility of Chlorine Gas?

The solubility of chlorine gas is 7.29 grams per liter at 68° F (20° C) and 1 atm. It dissolves almost instantly and completely in water.

Is Chlorine Gas stable?

No, chlorine gas is not stable. Chlorine gas is inherently unstable, and the more stable you try to make it, the more you must add to it, which increases its cost. It can be stabilized by sunlight through the addition of cyanuric acid. However, it is hazardous and can be lethal, requiring careful handling and storage. It is also heavier than air and can cause severe eye, nose, and throat irritation.

How to store Chlorine Gas?

Chlorine gas is typically stored in steel containers of various sizes. It requires special non-corrosive rooms with various safety measures such as scales, secondary containment, gas sensors, alarms, positive ventilation, self-contained breathing apparatus, leak detection equipment, and more. Permits from multiple agencies and fire departments are also necessary.  In more detail, chlorine gas is usually stored in 2000-lb., 150-lb., and 20-lb steel containers. These containers must be individually chained to the wall, and the regulator flow must be slow enough to prevent ice formation on the cylinder. The storage rooms for these containers must be non-corrosive and equipped with safety measures including scales for weight measurement, secondary containment for spill control, gas sensors and alarms for leak detection, positive ventilation for air circulation, and self-contained breathing apparatus for emergency situations. Leak detection equipment is also necessary to quickly identify and control any gas leaks. To store chlorine gas, permits must be obtained from multiple agencies and fire departments to ensure compliance with safety regulations.

What are the regulations for using Chlorine Gas?

The Food Quality Protection Act of 1996 (FQPA) regulates the use of chlorine gas in swimming pools. Each state can set minimum training requirements. To minimize poisoning risks, the EPA restricts its use in nonresidential pools to certified pesticide applicators or those under their direct control.

How does the EPA classify Chlorine Gas?

The EPA reclassified chlorine gas for nonresidential swimming pools from General Use to Restricted Use, based on incident reports. The certification for gas chlorine applicators is left to the states. For residential use, the EPA does not enforce restrictions, but the Department of Homeland Security has named chlorine gas a Chemical of Interest (COI).

How is Chlorine Gas Used?

Chlorine gas is used in various ways. In the pool industry, it is used for water treatment, although its use is becoming less common due to safety concerns. It is also used as a standard against which all other chlorine compounds are compared. In commercial pools, it is used as an efficient and cost-effective sanitizer. It is also used for regular and super chlorination as a primary sanitizer and disinfectant. Chlorine gas is applied to water using a diffuser, injector, or eductor. However, its use in residential pools has decreased due to potential EPA regulations.

How is Chlorine Gas Used in the Pool Industry?

In the pool industry, chlorine gas is typically stored in 2000-lb., 150-lb., and 20-lb steel containers. Some large, older swimming pools still use chlorine gas for water treatment. However, due to its dangers and public safety concerns, its use is becoming less common. To use chlorine gas today, special non-corrosive rooms with various safety measures are required. These include scales, secondary containment, gas sensors, alarms, positive ventilation, self-contained breathing apparatus, leak detection equipment, and more. Permits from multiple agencies and fire departments are also necessary.

How is chlorine gas used in commercial pools?

Chlorine gas is used in commercial pools as an efficient and cost-effective sanitizer. It is injected into circulating water, gradually adding chemicals to the pool or spa. The gas is supplied in cylinders that discharge it through a pressure regulator, volume control, and visible volume meter to a water reservoir. The gas mixes with the water to form a solution that is then pumped into the circulation system for delivery to the pool or spa.

What Chlorine Gas used in Residential Pools?

Chlorine gas was previously used in residential pools, with companies injecting it into the pool water weekly using 20-lb. steel chlorine cylinders. However, most have now switched to other types of chlorine due to public pressure and potential EPA regulations.

How to increase Chlorine in the pool with Gas Chlorine?

To increase chlorine in the pool with gas chlorine, the gas is injected into circulating water, gradually adding chemicals to the pool or spa. The gas is supplied in cylinders that discharge it through a pressure regulator, volume control, and visible volume meter to a water reservoir. The gas mixes with the water to form a solution that is then pumped into the circulation system for delivery to the pool or spa.

What Happens When Chlorine Gas is Added to Water?

When chlorine gas is added to water, it rapidly reacts to produce hypochlorous acid (HOCl). This acid then dissociates into hydrogen ion and hypochlorite ion. The effectiveness of HOCl, the faster killing form of chlorine in water, depends on the pH of the water.  When chlorine gas dissolves in water, it rapidly hydrolyzes according to this equation: Cl + H2O -> HOCl + H+ + Cl–. This means that chlorine gas and water produce hypochlorous acid, a hydrogen ion, and a chloride ion. Alternatively, this can be stated as chlorine gas and water yielding hypochlorous acid and hydrochloric acid, which then ionizes into a hydrogen ion and a chloride ion.

What are the Benefits of Chlorine Gas?

The benefits of chlorine gas include its cost-effectiveness, efficiency as a sanitizer for commercial pools, and its role as a standard against which all other chlorine compounds are compared. It is also 100% available and does not require a pH neutralizer.  Chlorine gas is popular due to its cost-effectiveness. A pound of chlorine gas costs around 90 cents, compared to  3.25 to 3.75 per gallon for liquid chlorine. It is an efficient and cost-effective sanitizer for commercial pools, where it is injected into circulating water, gradually adding chemicals to the pool or spa. Chlorine gas is the standard against which all other chlorine compounds are compared, having an oxidizing power of 100% and being pure, with a chlorine weight in the formula (Cl) of 100%. It is 100% available and does not require a pH neutralizer, making it a convenient choice for many applications.

How are chlorine products arranged?

Chlorine products are arranged in order of relative cost, with gas being the cheapest. The more stable you try to make this inherently unstable product, the more you must add to it and therefore the more expensive it becomes. Chlorine is 100% available and does not require a pH neutralizer. It has a pH of less than 1.0 and increases TDS by 30 ppm per 10,000 gallons, including pH neutralizer. It has an indefinite shelf life.