There are practices that inadvertently or purposely circumvent Stage I Vapor Recovery, adding pressure to the storage tank, reducing the effectiveness of, or bypassing Stage I Vapor Recovery entirely. For instance, there is often a common vent for all gasoline tanks at a facility (including E85). If two tanks are receiving drops at the same time, the single return of a typical Stage I vapor recovery system is no longer working as intended, causing saturated hydrocarbons to vent. There are delivery personnel that, intent on dropping fuel faster, open the truck vents or do not connect the tank vapor return to the truck. This allows faster filling, but little or no vapor return to the tank truck. In addition to adding potentially damaging pressure to the storage tank, venting gasoline hydrocarbons to the atmosphere exposes people within 1,000 feet to toxic levels of benzene and other carcinogens. Not something you want to see in the news.
With properly connected and functioning Stage I Vapor Recovery equipment, tanker truck fuel deliveries are a “dynamically balanced” system where little pressure (less than 2” wc) is exerted inside the fuel tank ullage. Operated as intended, saturated hydrocarbons are not vented into the atmosphere. Fuel storage tanks and other components are not damaged by high pressure in the tank UNLESS the fueling is terminated due to a ball float valve type overfill event. The use of ball floats can produce hydraulic shock of 20 psi or more on the tank.
Stage I Vapor Recovery Systems are Regularly, Intentionally or Inadvertently Defeated
The TPM-6200 is a two-part system consisting of a Pressure Sensor and Transmitter Module mounted on the tank’s vent riser and a Receiver, Recorder and Notification Module located inside the building in proximity to the site’s Automatic Tank Gauge.
There are two primary purposes of the TPM-6200:
1. Identify tank over-pressurizations due to tank filling operations. Notify the transport operator of the over-pressurization event within two minutes of event start. Time / Date stamp and report event. Tank over-pressurizations due to filling operations are usually the single largest cause of vapor releases at a station. These events are preventable.
2. Detect other vapor release events. Examples are, Open Tank Scenarios due to malfunctioning equipment such as P/V valves or non-tight fittings.
Alarm at Delivery Over-pressurizations
Up to now, Delivery Over-pressurizations were not identified by station monitoring equipment. Even CARB regulated stations did not have a specific Alarm for delivery over-pressurizations. Vml has developed how to rapidly identify (within 2 minutes) delivery over-pressurizations. The TPM responds with a strobe light and a horn to attract the driver’s attention. The signage clearly identifies the delivery pressure problem asking the driver to stop the over-pressurization.
Receiver Module Alarm
Located in the store, the Receiver Module has a green LED illuminated when the tank ullage pressure is normal. If a Delivery Over-pressurization event is detected, or other Alarm such as an Open Tank Scenario, the LED flashes red until the Alarm Log is looked at. The Alarm event can also be output to a tank monitor providing the potential for monitored sites to have immediate notification.