Tech Talk: “Flaring Propane 101”
Hazmat Nation has kicked off another “Tech Talk” segment sharing with hazmat teams and responders around the country.
This training topic is from Firefighter Ronald D. Huffman, Senior Instructor/Owner of
Responder Training, Inc.
Flaring or the burning of propane through a flare stack is done for multiple reasons. When the propane industry needs to service a tank or move it, they typically transfer the liquid to another tank and then burn off the remaining pressure. Responders on the other hand typically use flares to reduce a tanks volume or its internal pressure. This could be necessary due to some type of physical damage, a leak that can’t be stopped or to reduce the volume of a tank has been overfilled.
The bulk of the incidents that we respond to range from small cylinders to residential tanks (500 and 1000 gallon) and a small flare may be all you need given the tanks volume. There are a couple of caveats: first, if the tanks been overfilled the faster you can gain vapor space the better (liquid removal). Or depending on the type of incident, you may need to force auto‐refrigeration quickly to reduce internal pressure (vapor removal). In either case, time and temperature are your enemy. In these cases, the size of your flare matters a lot. The greater the flares capacity the quicker you can evacuate product and hopefully complete the task at hand safely.
When you think about flares ask yourself this, can you have too much capacity? The answer is no! Can you have more than you normally need, sure, and you should.
It doesn’t matter what size the tank is, your flaring operation will always be limited to the capacity of the piping and appliances installed. For example, connecting a 1” flare to a 20‐pound cylinder will not flow any more than the capacity of the valves and fittings installed. 29 CFR 1926.153 ‐ Liquefied Petroleum Gas states – “Systems utilizing containers having a water capacity greater than 2 1⁄2 pounds shall be equipped with excess flow valves”.
So, what is an “Excess Flow Valve”? Excess flow valves or EFV’s are in‐line devices designed to reduce the flow of product when extreme flow rates occur. An example would be when a system valve is opened too fast or when damage to the system occurs and allows more flow than the EFV is rated for. Once product flow exceeds the valves’ rated capacity the valve shuts or seats reducing the flow down to the bleed orifice that is drilled into the valve disk. Bulk storage tanks and transport vehicles are required to have either an internal valve with the excess flow device as part of its assembly, or an excess flow valve installed in the tank on any opening 3⁄4 of an inch or larger.
In most cases it’s difficult or impossible to distinguish between an excess flow valve and a check valve without verifying the manufacturer’s item number or specific knowledge of the installation. Both have very different jobs. While an excess flow valve allows product flow in both directions, a check valve only allows flow in one direction. If a flare is connected to a system and no or very limited pressure is accessible the line could have a check valve instead of an excess flow valve. Since October 1st 1998 all new small DOT cylinders (4 to 40 pound) have been required to have an Overfill Protection Device (OPD) installed.
OPD equipped cylinders utilize a QCC Type‐1 connector and product flow volumes are determined by the capacity of the connector not the valve itself. Type 1 connectors include the excess flow as an integral part of the connector.
Type 1 connectors are color coded to indicate flow capacities; black connectors can flow enough propane to produce up to 100,000 BTU per hour or BTUH, green to 200,000 BTUH and red to 400,000 BTUH.
See figure 4‐Type 1 Connectors
If flows are determined by the excess flow valves capacity the question is why would you want or need a flare large enough to exceed the system’s full flow capacity? That’s easy, volume. Not all incidents have the same flow restrictions. The larger the tank opening the greater the flow capacity. A lower volume flare would be sufficient for some incidents where rate of evacuation is not an issue. But, let’s say you have a tank and it’s been damaged, it’s venting its contents into the atmosphere and the vapors are accumulating on the ground. The longer it leaks the larger the hazard area will become.
Most departments have only a few tactical options available to them when they arrive on scene.
1) Identify the need for and contact additional resources.
2) Evacuate the immediate hazard area.
3) Manage product vapors by dispersing them with a fog stream. Maintain the process until the tank vents itself completely, or at least down to a safe pressure to start dealing with the problem. While continually monitoring downgrade and downwind for any signs of dangerous levels of propane vapor.
4) Under the protection of a fog stream gain access to the appropriate valving. Shut off the valve if possible and remove any nearby ignition sources that can be done safely.
5) Do 1 – 4 if possible and wait until qualified help arrives.
6) If it’s discovered that the leak cannot be stopped and you cannot accomplish 3 & 4, evacuate to a safe area and monitor downgrade and downwind.
This photo was taken during one such event. The dome of an underground storage tank was struck by a vehicle and the relief valve was broken off. The local VFD was dispatched and once on scene they
requested the local HazMat team. HazMat arrived on scene and requested that downwind and downgrade be evacuated, air monitoring was set up and the local propane company contacted. Once the propane supplier arrived their flare was set up to start burning off tank pressure and force auto‐refrigeration. A wooden plug was driven into the remaining relief valve stem to slow the leak. After the tanks pressure had dropped to a safe level, the plug was removed and repairs were made. The total operation took about 9 hours.
Let’s look at another call. It’s 08:30 hrs. and 65 degrees outside. The tones go off and you’re dispatched to a 10,000‐gallon bulk storage tank that had been overfilled the night before. It’s now intermittently releasing liquid from the relief valve. You arrive on scene and realize you’ll need to move a lot of product ASAP. To reduce the tanks volume down to where it should be (80%) you would need to remove 2000 gallons of propane. The sun’s rising and it’s expected to be 95 degrees by 13:00 hrs. You make the connections and open the appropriate valves and wait. Can you flow enough to keep ahead of the expanding product? Maybe, hopefully, no matter the size of your flare, you must start applying cooling streams to the tank. An incident such as this would be a candidate for a liquid and a vapor flare operating up wind, up hill and at a safe distance. If you can not keep ahead of the expanding propane a hydrostatic rupture is a possibility. Again, time and temperature are not your friend….
How do you know if the equipment you’re using is flowing all the system is capable of? If you can fully open the valve on a tank and the flare and not slam the excess flow, your system is probably not big enough. What you need is a flare that will allow you to remove as much product as possible, as quickly as possible. Flares range in size from small 1⁄2”pipe, flares that utilize industry standard 1” connections, large trailered flares (Figure 6) and fixed facility installations. No matter what system you use, you’ll always be balancing the tanks flow capability against the flares flow capacity.
Flaring Vapor vs Liquid
Liquid: Releasing liquid reduces a tanks volume much quicker than burning vapor allowing you to gain valuable vapor space. Propane dealers normally don’t flare liquid, propane is money and when servicing equipment is the goal, there is little to no reason to waste product. The liquid product is normally pumped out and a flare is set up to remove residual vapor pressure. Flaring liquid can and usually does pose a problem especially as the pressure decreases. Liquid can run down the flare stack and burn part if not all the way to the ground. The main burner of some flares are constructed from steel pipe and are not susceptible to flame damage as a result of run down like rubber hose. When flaring liquid responders have an option that the propane industry doesn’t, we usually have access to a fire engine. Dealing with small ground fires due to run down may just be the cost of quickly managing the propane emergency. Normally when responders are called it’s because of an emergency that most likely needs resolved or at least the bulk of the hazard elevated as quickly as possible. When a tank has been over filled flaring liquid will gain vapor space much faster than burning vapor.
Vapor: But, if the incident requires you to reduce internal pressure as quickly as possible flaring vapor will most likely be your best option. The benefit of this tactic will be lowering of the internal pressure to a level where it may be safe to repair a leak as explained above. If you intend to completely evacuate the tank start with liquid if possible. As you can see in Table 1 the lower the propane temperature the lower the vapor pressure. When vapor and to a smaller extent liquid is released from a tank the propane boils causing auto‐refrigeration that results in a pressure drop. In some instances, depending on the volume of propane in the tank and your flares capacity it may take a while for the flaring operation to produce the needed result.
When faced with a propane emergency one of your first questions must be, do I need to create vapor space by flaring liquid, or do I need reduced vapor pressure by forcing auto‐refrigeration? What’s the real hazard? Has the tank been overfilled and you need vapor space to stop a hydrostatic rupture? Or do you need to reduce vapor pressure so that a broken fitting can be changed out?
Utilizing a flare to reduce a tanks volume or internal pressure in cooperation with other tactical options should always be a consideration. Your best tactic might be two flares: one connected to liquid to start gaining vapor space and a second to reduce vapor pressure forcing auto refrigeration and reducing internal pressure. Operating at a small flares capacity is easy, you can open the valves completely and probably not activate the excess flow valve. But remember the longer the propane leaks the greater the potential of a vapor ignition. If you have a limited volume flare what happens when you respond to a bobtail, tanker or bulk storage tank that has pipe and fittings that have the capacity to flow larger volumes but your flare can’t? This is where size really matters. If your flare has the capacity to flow more volume than the tanks excess flow valve is capable of you’ll need to adjust the flow rate down to reach maximum propane transfer just prior to the excess flow valve activating.
To accomplish this, you may need to play with the system for a minute to find the sweet spot. Light the flares pilot burner, slowly open the systems valve until the excess flow slams. Identify the valve position and shut the valve. Once the excess flow valves disk opens back up (you should hear a click) make sure your pilot flame is burning and open the system valve just short of slamming the excess flow again.
Flaring is a tactical option that at a minimum all hazardous material teams should have in their tool box, the same could be said for fire departments. Most if not all HazMat teams carry a “C” kit for the possibility of a leaking Chlorine container. But how many carry a flare for propane incidents capable of a full 1” flow (see Figure 2‐1)? If you think about it, when was the last time you were on a chlorine release verses a propane incident. LP trucks run up and down our roads every day. Homes, business and industry have bulk storage tanks that provide heat or manufacturing support. Each and every propane container has the potential to leak, are you ready? Contact Ron Huffman by clicking here.
When it comes to flaring capabilities
“It’s better to have and not need, than to need and not have!”
*Editors note, it always a good idea to make sure you have some sort of relationship with a propane company that can assist you regardless of who is the owner of the tank & fuel is. An “ounce of prevention” as they say