What to Know About Flame Arrestors?
Backflash controls are a necessary safety device used in applications dealing with the potential for ignition of flammable gas-air mixtures (i.e. methane, propane, oxygen etc. ). These engineered control devices are installed to stop the propagation of flame out of the intended area, ultimately protecting people, equipment and property.
In many jurisdictions, combustors are required to use flame arresting devices on close spacing applications. For example:
- The Alberta Energy Regulator (AER) lists this requirement in Directive 60, section 7.1.3, e) All intakes must be equipped with a flame arresting device.
- The Saskatchewan MRO 60/20 states:Waste gas, pilot gas and air intakes must be equipped with flame arrestors devices. The flame arrestor must:
- Meet the requirements of ISO 16852:2016 Flame Arrestors; or
- The air intake must be located at least 3 meters from a class 1, division 1 or 2 hazardous areas as per SaskPower’s Code for Electrical Installations at Oil and Gas Facilities.
Are There Different Types of Flame Arrestors?
There are several different flame arrestors developed over the years. Extensive research on these control devices has given a good understanding of the principles used in each technology.
Flame Screen or Gauze
The flame screen, was brought to industry by Sir Humphry Davies to be used in miner’s safety lamps and is the first documented flame arrestor. Miners worked in the underground in coal mines, where there was a potential to be exposed to flammable gases, and it was essential to shield the miners flamed lamps with backlash protection.
The screens typically consist of a single screen of corrosion-resistant wire of at least 30 by 30 mesh or two fitted screens, both of corrosion-resistant write of at least 20 by 20 mesh spaced not less than one-half inch or more than 1-1/2 inches apart. (US Coast Guard,46 CFR 151.03-25).
Flame screens are used in many applications today for backflash control, mainly on fuel storage tanks on large transport ships. They are excellent flame arresting devices for atmospheric conditions where the flame speed is low (<10 m/s) (K.N. Palmer and S. Tonkin, 1958).
Crimped ribbon arrestors are the most common and widely used flame arrestors. They are typically constructed by winding alternate layers of crimped and plain metal ribbon surrounded by suitable housing. These construction methods provide reasonable control of the size and depth of the holes. However, due to their design, the crimped ribbon arrestor needs to be supported on both sides of the arrestor.
Compressed Wire Wool
The device is made by compressing a mass of fine wire or knitted wire into a holder. This type of technology has been effectively used in acetylene filling plants to protect the compressor and the cylinders. However, this device has a high resistance to gas flow, limiting its applications (H. Phillips and D.K Pritchard). In addition, the effectiveness of this type of arrestor decreases as the compression increases.
These arrestors consist of a housing filled with loose discrete objects held by restraining screens or gravity. This type of arrestor’s effectiveness depends on the material used, the spacing between materials, and the depth of filling (H. Phillips and D.K Pritchard). This type of arrestor typically bulky to stop flames fast. They have traditionally been used in the chemical industry.
Other Flame Arrestors
Several different methods of stopping flame propagation are not touched on in this Blog (i.e. Expanded Metal, Perforated Sheet, Sintered Metal, Metal Foam, Hydraulic, Stacked Parellel Plates).
How do Flame Arrestors Stop a Flame?
Flame arrestors work by extinguishing the flame, preventing flame propagation to the other side of the arrestor. This process works under heat loss principles (N.A.Kakutkina, A.A. Korzhavin, A.D.Rychkov, 2009). By removing the heat needed for a flame, the flame cannot continue to the other side of the arrestor.
A flame requires three inputs; Heat, Oxygen, fuel, collectively referred to as the fire triangle. If any of these (3) ingredients are removed, the flame cannot continue.
How to Test Flame Arrestors?
Flame arrestors are typically required to meet specific standards (i.e. ISO 16852:2016, US Coast Guard, UL 525) designed by engineers.
To ensure that the flame arresting devices is suitable for the application, the Engineer may choose to test the devices using the test methods outlined in API 2028 – Flame Arresters in Piping Systems and API 12N – Recommended Practice for the Operation, Maintenance and Testing of Firebox Flame Arrestors
How to Choose a Flame Arrestor
Choosing a flame arrestor is best completed by a qualified engineer. There are a several considerations to make for each application to ensure that the flame arrestor provides the proper protection (i.e. pressure, air flow, applicable gases, nearby equipment).
- Davy, Sir H., 1816, Philosophical Transactions.
- Palmer, K.N. and Tonkin, P.S., 1958, Seventh International Symposiumon Combustion, Combustion Institute, Pittsburg, USA.
- Phillips, D.K. Pritchard, Performance Requirements of Flame Arrestors in Practical Applications
- A.Kakutkina, A.A. Korzhavin, A.D.Rychkov, 2009,. Burning-through Porour Flame Arrestos with a Channel Flame-Arrester Element. Combustion, Explosion, and Shock, Vol 45, No.3
- API 12N, 2nd Edition, 2000,. Recommended Practice for the Operation, Maintenance and Texting of Firebox Flame Arrestors