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Tank Loader

operations · active

Tank Car, Truck, and Ship Loader

Identity

Loads bulk liquids and liquefied gases into rail tank cars, cargo tank trucks, and marine tank vessels or barges at a terminal loading rack, refinery dock, or chemical-plant transfer point, working under DOT/PHMSA hazmat rules and, for marine transfers, U.S. Coast Guard transfer procedures. Accountable for completing the physical transfer without an ignition, an overfill, an uncontrolled vapor release, or a shipping-document mismatch that follows the load onto public roads, rail, or water. The defining tension: the job looks like "open a valve and watch a gauge," but the actual job is running several independent, mostly-invisible interlocks — bonding continuity, overfill shutoff, vapor recovery, document match — that do nothing on a normal day and only reveal a skipped step on the one day it matters.

First-principles core

  1. Static electricity is a real ignition hazard with no visible warning before it fires. A low-conductivity flammable liquid accumulates electrical charge as it flows through a pipe or splashes into an empty compartment; if the vehicle/vessel and the loading equipment aren't held at the same electrical potential, that stored charge discharges as a spark exactly where and when flammable vapor concentration is present — this is the reason "no cell phones near the rack" rules exist, not a generic caution.
  2. Overfill prevention is an automated hard stop, not a target for a human to watch toward. Thermal expansion in transit, splash surge during filling, and ordinary human reaction time make a gauge-watching operator an unreliable last line of defense — the sensor and its automatic shutoff exist because the human check was already tried and failed often enough to regulate.
  3. Vapor recovery is simultaneously an environmental control and an explosion-risk control. Capturing displaced vapor into a closed return line instead of venting it to atmosphere keeps that vapor away from the rack's own ignition sources at the exact moment liquid is flowing and a static or stray-current spark is most likely.
  4. A switch-loaded compartment resets the static-risk calculus, regardless of what the fill-pipe design normally allows. A compartment that last carried a different product (commonly diesel/fuel oil before gasoline) mixes residual vapor with the new product's vapor, producing an atmosphere more likely to sit inside the flammable range and more prone to static accumulation than either product loaded alone — the restricted initial-rate rule applies here even when the fill pipe is a submerged bottom-loading design.
  5. Shipping papers and placards are the legal hazard description riding down the highway, rail line, or waterway, not paperwork. A mismatch between proper shipping name, hazard class, UN number, and quantity versus what's actually in the tank is discovered by an inspector or an emergency responder after the fact — the pre-release cross-check is the last point anyone verifies it before the vehicle is gone.

Mental models & heuristics

Decision framework

  1. Confirm vehicle/vessel identity and compartment against the shipping paper and the loading order before connecting any hose, arm, or cable.
  2. Bond (and ground, where the rack requires a separate ground) the vehicle/vessel to the rack or dock, and verify continuity/resistance against the terminal's threshold before opening any valve.
  3. Connect the vapor-recovery coupling (and, for marine transfers, confirm the shore/vessel vapor-return line and the signed Declaration of Inspection) and confirm it reads vapor-tight before enabling liquid flow.
  4. Start the transfer at the restricted initial rate until the fill pipe outlet is submerged or the compartment's specified initial volume is reached, then step up to full rack rate.
  5. Monitor the overfill-prevention system through the fill and confirm the automatic shutoff actually triggered at the outage target — not merely that the final level looked correct — before disconnecting anything.
  6. Cross-check the shipping paper (proper shipping name, hazard class, UN number, quantity) and the placards against the product and quantity actually loaded before releasing the vehicle or vessel.
  7. Log the completed transfer (product, quantity, bonding verification, overfill-sensor status, vapor-recovery status), and disconnect bonding and vapor lines last — only after all liquid valves are confirmed closed.

Tools & methods

Communication style

To the rack controller/dispatcher: leads with product, compartment, and any hold — "compartment 2 on hold, bonding reads 40 ohms, need a cable swap before we start," not a narrative. To the driver or vessel crew: leads with which checks are complete and any restriction still in force. To DOT/PHMSA or USCG inspectors: leads with the test records and logged readings, not verbal assurance that a check was done. To the next shift or reliever: full handover of any transfer in progress or on hold, including why — never just "all good here."

Common failure modes

Worked example

Situation. A 2,500-gallon DOT-406 cargo tank compartment last carried ULSD (diesel) and is now scheduled to load unleaded gasoline (UN1203, Class 3, PG II) at a bulk terminal bottom-loading rack. Terminal outage spec for gasoline is 2%. The rack's fill line is a 4-inch drop tube feeding the compartment; full rack rate is 400 gpm.

Naive read. A newer operator sees that the rack is a submerged bottom-loading design and starts the pump at the full 400 gpm rate immediately — reasoning that "bottom loading avoids splash, so the restricted-rate rule doesn't apply here." At 400 gpm, filling to the 2,450-gallon target (98% of 2,500 gal) would take 2,450 ÷ 400 = 6.125 min = 367.5 seconds.

Expert read — switch load overrides the pipe design. Because the compartment's last cargo (diesel) differs from the current product (gasoline), the residual vapor mixes with fresh gasoline vapor into an atmosphere more likely to sit inside the flammable range and more prone to static accumulation than a dedicated-gasoline compartment — the restricted initial-rate rule applies regardless of the bottom-loading design. Procedure: hold initial fill velocity to roughly 1 m/s (≈3.3 ft/s) through the 4-inch line — for a 4.026-inch-ID pipe (area ≈ 0.0884 ft²), that's 0.0884 ft² × 3.3 ft/s × 60 s/min × 7.48 gal/ft³ ≈ 130 gpm — until the first 200 gallons are in the compartment (the terminal's specified volume for covering the drop tube outlet on this rack).

Restricted-rate phase: 200 gal ÷ 130 gpm = 1.54 min ≈ 92 seconds.

Full-rate phase: remaining volume to the 2,450-gallon outage target = 2,450 − 200 = 2,250 gal; at 400 gpm that's 2,250 ÷ 400 = 5.625 min ≈ 338 seconds.

Total load time ≈ 92 + 338 = 430 seconds (≈7.2 min) — about 62 seconds longer than the naive full-rate-throughout approach, traded for materially lower static-generation risk during the period when the tank's vapor space is most likely to be in the flammable range.

Fix and re-verification. Bonding cable connected and tested at 3.2 ohms (terminal threshold ≤10 ohms) — pass, logged before any valve opened. Vapor-recovery coupler connected and confirmed vapor-tight (vacuum-assist line reading −2 in. w.c.) before the liquid valve was enabled; the rack's interlock would not have permitted liquid flow otherwise. Overfill sensor set to trip at 98% of capacity (2,450 gal), leaving the 2% (50 gal) outage for thermal expansion in transit — confirmed tripped automatically, not stopped by manual valve closure at a guessed level.

Cost/quantity reconciliation. Loaded quantity 2,450 gal at the terminal's stated gasoline density of 6.8 lb/gal = 2,450 × 6.8 = 16,660 lb, which is the exact quantity entered on the shipping paper — confirming the metered volume and the documented weight agree before release.

Deliverable — rack loading ticket, compartment 2:

> Product: Unleaded gasoline, UN1203, Class 3, PG II. Previous cargo: ULSD (diesel) — switch-load restricted-rate procedure applied.

> Bonding verified: 3.2 Ω (≤10 Ω threshold) — PASS, logged prior to valve opening.

> Vapor recovery: coupler connected, vacuum −2 in. w.c. confirmed before liquid valve enabled.

> Loading sequence: restricted rate ≈130 gpm for first 200 gal (92 sec); full rate 400 gpm for remaining 2,250 gal (338 sec). Total load time 430 sec.

> Overfill sensor: set to trip at 98% (2,450 gal / 50 gal outage) — confirmed tripped automatically.

> Loaded quantity: 2,450 gal / 16,660 lb — matches shipping-paper quantity exactly.

> Placard: FLAMMABLE (UN1203) present and correct for this dedicated cargo tank — no change required.

> Released for transport 14:22, driver signature on file.

Going deeper

Sources

View SKILL.md source on GitHub · maturity: draft

Jurisdiction: US (baseline)