Occupational Health & Safety

Securing Industrial Chlorine Supplies

Improved fire codes allow use of fail-safe valves, easing storage and use requirements for chlorine gas.

USERS of chlorine now regulated by the newly created 2003 International Fire Code and the 2003 Edition of the Uniform Fire Code are pleased to find they are no longer required to have a scrubber when storing or using 150-lb cylinders or one-ton containers of liquefied chlorine gas.

A scrubbing system usually consists of a scrubbing chemical (typically, caustic soda) and a blower to draw contaminated air through the caustic solution being circulated by use of a pump.

For indoor and outdoor storage, the need for a scrubber is eliminated if . . .

1. Chlorine cylinder valve outlets are equipped with gas-tight outlet plugs or caps.

2. Where approved containment vessels or containment systems capable of fully containing or terminating a release are available or that are capable of being transported to the leaking cylinder, container, or tank.

For indoor and outdoor use, the need for a scrubber is eliminated if . . .

1. An approved, automatic-closing fail-safe valve is located immediately adjacent to and downstream of the active cylinder valves. The fail-safe must close when gas is detected at the permissible exposure limit (PEL) by a gas detection system monitoring the exhaust system at the point of discharge from gas cabinet, exhausted enclosure, ventilated enclosure, or gas room.

2. Where approved containment vessels or containment systems capable of fully containing or terminating a release are available or that are capable of being transported to the leaking cylinder, container, or tank.

Plant operators have found that fail-safe valves and containment vessels require little or no maintenance, repair, or replacement. According to Maui Plant Operator Wayne Fujiwara, "Total containment is easier to use than a scrubber. It does what it says it will do, and we don't have to worry about leaks."

A scrubber system may require extensive maintenance, repair, and replacement, including testing of caustic solution, replacement of caustic, instrument calibration, belt adjustments, sheave alignment, scrubbing chemical feed pump adjustments, exhaust air fan adjustments, fan wheel service, pump seal replacement, and pump rebuilds and replacement. A fail-safe valve is typically described as a 1/4 turn ball valve that is spring loaded, always fails in a closed position, and does not rely on any electrical power or backup emergency power to close the valve. A valve that does not have all these characteristics is unsafe by comparison.

Ensuring Operators' and the Public's Safety
Unmanned sites located in densely populated areas are especially in need of a system to process chlorine from cylinders or ton containers that will release little or no chlorine gas to the surrounding community.

Total containment vessels used for processing chlorine from a cylinder or ton container that is enclosed within the vessel are the only system that reduces the worst-case off-site release of toxic gas by 97 percent, making it by far the safest method for processing chlorine.

" 'Passive' was a selling point to me," said Ellis DeWell, assistant plant superintendent in Springfield, Ohio. "It made a very important difference since we are governed by the EPA rules and regulations."

Scrubbers and fail-safe shutdown valves provide no reduction in the off-site area affected when conducting RMP studies to assess the effects of a release to the surrounding community. Consulting engineer George Clifford White, author of the "Handbook of Chlorination and Alternative Disinfections, Fourth Edition," said total containment is the "safest and most cost-effective" treatment system available today.

Rick Roll of North Little Rock, Arkansas' water treatment plant chose total containment, as well. "Safety for our operators and the surrounding area was the primary concern," he said. "The locking door adds extra security from prying hands. It seems to be a foolproof system. Simplicity is the best ticket."

Sites located within sparsely populated areas may find the cost of installing a scrubber system or total containment system used for the processing of cylinders or ton containers to be out of the question because of budget constraints. The new codes allow these sites to use the less expensive automatic closing fail-safe shutdown valves located immediately adjacent to the cylinder valves. The fail-safe valves must close when a gas detection system detects a release at the permissible exposure limit.

All sites storing cylinders or ton containers must have available to them containment vessels or systems capable of fully containing or terminating a release from a leaking cylinder or container. If the emergency containment vessel is not located at the site, it must be capable of being transported to the site of the leaking cylinder. A trailer mounted emergency containment vessel would typically be transported to the site of the leaking cylinder or container by the emergency responder.

Options for Communities with Multiple Sites
Communities with multiple sites need have only one emergency vessel available to them to handle leaking cylinders or containers. However, locating an emergency vessel at every site will provide added safety.

The emergency vessel must be designed to process the entire contents of the leaking cylinder or container at the treatment site to prevent transporting a leaking cylinder or ton container. Small communities may, by an association with others, share the cost of a containment vessel system, one that is trailer mounted, to allow compliance at a lower cost.

Total containment vessels satisfy the definition of a treatment system in the codes because, once contained within the vessel, the total contents from the leaking cylinder or ton container can be put into process at the site at a safe, controlled rate.

As in all cases related to fire codes, consult the local fire department to determine its requirements.

Referenced Code Issues

1. 2003 International Fire Code Chapter 37, Highly Toxic and Toxic Materials

2. 2003 Uniform Fire Code Chapter 55, Standard For The Storage, Use And Handling Of Compressed Gases And Cryogenic Fluids In Portable And Stationary Containers, Cylinders And Tanks

Definitions
IFC: 3702.1, Containment Vessel
UFC: 3.3.12, Cylinder Containment Vessel
Both read: "A gas-tight recovery vessel designed so that a leaking compressed gas container can be placed within its confines thereby encapsulating the leaking container."

IFC: 3702.1, Containment System
UFC: 3.3.33.3, Cylinder Containment System
Both read: "A gas-tight recovery system comprised of equipment or devices which (that) can be placed over a leak in a compressed gas container, thereby stopping or controlling the escape of gas from the leaking container."

Treatment System
IFC: 3704.2.2.7.1, Treatment System Design
"Treatment systems shall be capable of diluting, adsorbing, absorbing, containing, neutralizing, burning, or otherwise processing the contents of the largest single vessel of compressed gas. Where a total containment system is used, the system shall be designed to handle the maximum anticipated pressure of release to the system when it reaches equilibrium."

IFC: 3704.2.2.7.2, Treatment System Performance
"Treatment systems shall be designated to reduce the maximum allowable discharge concentrations of the gas to one-half immediately dangerous to life and health (IDLH) at the point of discharge to the atmosphere. Where more than one gas is emitted to the treatment system, the treatment system shall be designated to handle the worse-case release based on the release rate, the quality and the IDLH for all compressed gases stored or used."

UFC: 7.9.3.3, Treatment System Design and Performance
"Treatment systems shall be capable of diluting, adsorbing, absorbing, containing, neutralizing, burning, or otherwise processing stored or used toxic or highly toxic gas, or both.
A) Where a total containment system is used, the system shall be designed to handle the maximum anticipated pressure of release to the system when it reaches equilibrium.
B) Treatment systems shall be capable of reducing the allowable discharge concentrations to one-half the immediately dangerous to life and health threshold at the point of discharge."

Gas Cabinet/Exhausted Enclosure Exception
IFC: 3704.2.2.3, Leaking Cylinders and Tanks
"One or more gas cabinets or exhausted enclosures shall be provided to handle leaking cylinders containers or tanks.
Exceptions:
1. Where cylinders, containers or tanks are located within gas cabinets or exhausted enclosures
2. Where approved containment vessels or containment systems are provided in accordance with all of the following:
2.1 Containment vessels or containment systems shall be capable of fully containing or terminating a release
2.2 Trained personnel shall be available at an approved location.
2.3 Containment vessels or containment systems shall be capable of being transported to the leaking cylinder, container or tank."

Treatment System Exceptions
IFC: 3704.2.2.7, Treatment Systems

"Exceptions:
1. Highly toxic and toxic gases--storage. A Treatment system is not required for cylinders, containers and tanks in storage when all of the following controls are provided:
1.1 Valve outlets are equipped with gas-tight outlet plugs or caps.
1.2 Handwheel-operated valves have handles secured to prevent movement.
1.3 Approved containment vessels or containment systems are provided in accordance with section 3704.2.2.3."

UFC: 7.9.3.1, Storage of Toxic or Highly Toxic Gases
"Treatment system shall not be required for toxic or highly toxic in storage where containers, cylinders, and tanks are provided with the controls specified in 7.9.3.1.1 through 7.9.3.1.3."

UFC: 7.9.3.1.1, Valve Outlets Protected
"Valve outlets shall be equipped with outlet plugs or caps, or both, rated for the container service pressure."

UFC: 7.9.3.1.2, Handwheel Secured
"Where provided, handwheel-operated valves shall be secured to prevent movement."

UFC: 7.9.3.1.3, Containment Devices Provided
"Approved cylinder containment vessels or cylinder containment systems shall be provided at an approved location."

Fail-Safe Valve
IFC: 3704.2.2.7, Treatment Systems
"Exceptions:
2. Toxic gases--use. Treatment systems are not be required for toxic gases supplied by cylinders or portable tanks not exceeding 660 gallons (2,498 liters) liquid capacity when the following are provided:
2.1 A gas detection system with a sensing interval not exceeding 5 minutes.
2.2 An approved automatic-closing fail-safe valve located immediately adjacent to cylinder valves. The fail-safe valve shall close when gas is detected at the permissible exposure limit (PEL) by a gas detection system monitoring the exhaust system at the point of discharge from the gas cabinet, exhausted enclosure, ventilated room or gas room. The gas detection shall comply with Section 3704.2.2.10."

UFC: 7.9.3.2.2, Fail-Safe Automatic Closing Valve
"An approved automatic-closing fail-safe valve shall be located immediately adjacent to and downstream of active container, cylinder, or tank valves.
A) The fail-safe valve shall close when gas is detected at the permissible exposure limit, short-term exposure limit (STEL), or ceiling limit by the gas detection system."



Comparison of Available Options


Fail-Safe Valve

Scrubber

Total Containment Vessel

Requires little or no repair, maintenance or replacement

yes

no

yes

Can be used to handle a leaking cylinder

no

yes

yes

Will handle release from cylinder fuse plug

no

yes

yes

Can be used at outdoor site

yes

no

yes

Can be considered passive mitigation

no

no

yes

Backup emergency power required

no

yes

no

Is considered a treatment system

no

yes

yes

Acceptable to EPA as mitigation measure to reduce off-site consequences

no

no

yes

Will handle a leak from cylinder valve stem

no

yes

yes

Will handle a leak from sheared-off cylinder valve

no

yes

yes

Encloses operators within toxic environment

no

yes

no

Requires the facility to maintain a six-man emergency response team on site

no

yes

no

Easy to install

yes

no

yes

Generates hazardous waste

no

yes

no

This article appears in the April 2005 issue of Occupational Health & Safety.

This article originally appeared in the April 2005 issue of Occupational Health & Safety.

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