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, gas chlorine 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. Chlorine gas is also known as “liquid chlorine” or “liquefied chlorine gas” outside the pool industry. Chlorine gas is hazardous and causes irritation to the eyes, nose, and throat. It is lethal in extreme cases. Despite its dangers, chlorine gas 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. Chlorine gas lowers the pH of water when introduced. Chlorine gas is 100% available, meaning it is completely accessible and ready to perform its function of reducing the pH. On the other hand, chlorine gas is difficult to operate and potentially lethal. Chlorine gas causes severe eye, nose, and throat irritation and in extreme cases, it is lethal. Chlorine gas is highly soluble in water.

How is Chlorine Gas Produced?

Chlorine gas is primarily produced using three types of electrolytic cells: diaphragm, mercury, and membrane. Chlorine gas 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 the weight of chlorine (Cl) in its composition amounting to a complete 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. Chlorine Gas dissolves almost instantly and completely in water.

Is Chlorine Gas stable?

No, chlorine gas is not stable. Chlorine gas is inherently unstable and any efforts to stabilize it inevitably require the addition of more substances, thereby leading to an increase in its overall cost. Sunlight, in conjunction with the introduction of cyanuric acid, is used to achieve the stabilization of chlorine. However, chlorine gas is hazardous and lethal, requiring careful handling and storage. Chlorine gas is also heavier than air and causes severe eye, nose, and throat irritation.

How to store Chlorine Gas?

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 sets minimum training requirements. In order to reduce the chances of poisoning, the U.S. Environmental Protection Agency (EPA) limits the usage of chlorine gas in nonresidential pools exclusively to certified pesticide applicators or individuals directly supervised by them.

How does the EPA classify Chlorine Gas?

Based on incident reports, the EPA reclassified chlorine gas for nonresidential swimming pools from General Use to Restricted Use. Individual state authority has the responsibility of certifying individuals or entities to handle chlorine gas. 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. Chlorine gas is also used as a standard against which all other chlorine compounds are compared. In commercial pools, chlorine gas 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, the use of chlorine gas 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, the use of chlorine gas is becoming less common. Today, to use chlorine gas, special non-corrosive rooms equipped 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 required for using chlorine gas.

How is Chlorine Gas used in commercial pools?

Chlorine gas is used in commercial pools as an efficient and cost-effective sanitizer. Chlorine 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. Chlorine gas mixes with the water to form a solution that is then pumped into the circulation system for delivery to the pool or spa.

How was 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 of them 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 separates 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 is expressed as chlorine gas and water creating hypochlorous acid and hydrochloric acid, which in turn ionizes to form 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. Gas chlorine 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. Gas chlorine 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 gas chlorine an optimal selection for many applications.

How are chlorine products arranged?

Chlorine products are arranged in order of relative cost, with gas being the cheapest. As more attempts are made to stabilize this naturally unstable product, it necessitates the addition of more substances, ultimately increasing its overall cost. Chlorine is 100% available and does not require a pH neutralizer. Chlorine has a pH of less than 1.0. Chlorine raises the concentration of total dissolved substances (TDS) by 30 parts per million (ppm) for each 10,000 gallons, including pH neutralizer. Chlorine has an indefinite shelf life.