Ethanol Load After Gasoline: Overfill Sensor and Tank Cleanliness Decision
At 06:40 a driver arrives at a terminal with a 4,200-gallon DOT-406 aluminum cargo tank divided into four compartments rated 1,200, 1,100, 1,100, and 800 gallons. The previous load was 3,500 gallons of regular gasoline, unloaded 18 hours earlier; the tank was drained but not washed. The next order is 3,600 gallons of denatured ethanol (UN1170, Class 3). During the pre-load walkaround the driver finds the rear 800-gallon compartment’s overfill sensor fails the terminal’s test, the 4-inch API coupler dust cap is missing, and the vapor-recovery hose gasket is cracked. The rack’s overfill protection system will not authorize loading any compartment unless every sensor passes. The driver also notices a faint gasoline odor and a small amount of liquid in the sight glass of the first compartment. The terminal has a repair bay but it is 90 minutes out of route; the customer is waiting. Dispatch says the load must go.
1. What should the driver do about the failed overfill sensor and the missing dust cap before loading?
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The overfill sensor is a safety interlock, not a convenience. The terminal’s system will not authorize loading because it cannot verify that the compartment is not overfilled; taping, bypassing, or guessing defeats the protection and can cause a spill through the vent. The missing dust cap exposes the API coupler to dirt and water and allows product to remain in the adapter; it must be replaced with the correct cap, not a rag. The cracked vapor gasket will leak vapor and can prevent vapor recovery from working. The correct decision is to have the bay replace the cap and gasket and repair or verify the sensor. If the bay cannot repair the sensor before the customer window closes, the driver may load only the three serviceable compartments if the terminal and dispatch authorize a partial load, and must not load the 800-gallon compartment. If dispatch insists on the full 3,600 gallons, the driver should refuse the load; the risk of an overfill release is not offset by the schedule.
2. How should the driver evaluate the gasoline residue and the liquid in the sight glass before loading ethanol?
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Ethanol is hygroscopic and is not compatible with water; free water can cause phase separation and leave a flammable layer, and gasoline residue can contaminate the product and affect quality. The sight glass liquid could be water from condensation or gasoline left in the line; the driver cannot assume it is harmless. The faint gasoline odor after 18 hours is expected from residual vapor, but the tank was only drained, not washed. The driver should drain the sight glass into a labeled container, determine what it is, and inspect the tank interior if access is available. If water is present or the tank cannot be verified clean and dry, the driver should reject the ethanol load and require a wash. Loading ethanol over water or gasoline residue without verification is a product-quality and safety problem, not just a paperwork issue.
3. If the terminal authorizes loading only the three serviceable compartments, what volume is available and what documentation and load-distribution actions are needed?
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The three serviceable compartments total 1,200 + 1,100 + 1,100 = 3,400 gallons, so the driver can load at most 3,400 gallons, 200 gallons short of the order. At about 6.6 lb/gal, 3,400 gallons weighs about 22,440 lb, which is within the tank and tractor ratings, but the driver must still check axle loads and compartment distribution. The bill of lading and shipping paper must show 3,400 gallons, not 3,600, and the customer and dispatch must be told. The 800-gallon compartment must remain closed and clearly identified as out of service. If the customer needs the full 3,600, the driver must wait for the sensor repair or a replacement trailer. Loading the extra 200 gallons into a compartment with a failed sensor would create exactly the overfill hazard the interlock is designed to prevent.