Pipeline Transportation
In North America, hazardous materials are commonly transported through millions of miles of pipelines. Products include natural gas, natural gas liquids, crude oil, gasoline, diesel, anhydrous ammonia, carbon dioxide, jet fuel, and other commodities. Most pipelines are buried, but above-ground structures and markers indicate their presence.
Types of Pipelines
Natural Gas Pipelines
- Natural Gas Transmission Pipelines. Large-diameter steel pipelines carrying flammable natural gas at 200 – 1,500 psi. Gas in transmission lines is odorless — generally not odorized with mercaptan. Gas containing hydrogen sulfide (H₂S) will have a distinct "rotten egg" odor.
- Natural Gas Distribution Pipelines. Smaller-diameter, lower-pressure lines of steel, plastic, or cast iron delivering gas to customers. Distribution gas is odorized with mercaptan (the "rotten egg" smell).
- Natural Gas-Gathering / Well Production Pipelines. Collect raw natural gas from wellheads to processing plants. Not odorized with mercaptan; may contain hydrogen sulfide (H₂S).
Hazardous Liquid and Highly Volatile Liquid Pipelines
- Hazardous Liquid Pipelines. Crude oil, refined petroleum products (gasoline, kerosene, jet fuel, diesel), and hazardous liquids (anhydrous ammonia, ethanol). A single line may transport different products in sequential "batches."
- Highly Volatile Liquid (HVL) Pipelines. Hazardous liquids that form a vapor cloud when released and have a vapor pressure exceeding 276 kPa (40 psia) at 37.8 °C (100 °F). Example: liquid propane.
Pipeline Markers
Because pipelines are usually buried, above-ground markers indicate their presence. Only transmission pipelines are marked — distribution and gathering pipelines are typically not marked with above-ground signs.
Markers warn that a transmission pipeline is present in the area, identify the product being carried, and provide the pipeline operator's name and 24-hour emergency phone number. They appear at frequent intervals along the right-of-way and at prominent points where the line crosses streets, highways, railways, or waterways.
A marker only indicates presence — it does not indicate exact location. Pipeline location within a right-of-way may vary along its length, and multiple pipelines may share the same right-of-way.
Marker Colors and Standard Fields
Markers carry four standard pieces of information:
| Field | Detail |
|---|---|
| Warning | e.g. "WARNING — Petroleum Pipeline", "CAUTION — Gas Pipeline" |
| Product | Natural gas, crude oil, gasoline, anhydrous ammonia, etc. |
| Operator | Name of the pipeline company |
| Emergency phone | 24-hour number to call for leaks, damage, or emergencies |
Additional variants
- Markers for pipelines transporting materials with dangerous levels of hydrogen sulfide (H₂S) may say "Sour" or "Poison."
- Natural gas distribution pipelines are not marked with above-ground signs.
- Gathering / production pipelines are often not marked with above-ground signs.
Pipeline Structures (Above Ground)
| Pipeline type | Above-ground structures |
|---|---|
| Natural gas transmission | Compressor stations, valves, metering stations |
| Natural gas distribution | Regulator stations, customer meters and regulators, valve box covers |
| Natural gas gathering / well production | Compressor stations, valves, metering stations, wellheads, piping, manifolds |
| Petroleum & hazardous liquids | Storage tanks, valves, pump stations, loading racks |
Indications of a Pipeline Leak or Rupture
Releases can range from minor leaks to catastrophic ruptures. Gases and liquids behave differently once released. General indications:
- Hissing, roaring, or explosive sound
- Flames appearing from the ground or water (possibly very large)
- Vapor cloud, fog, or mist
- Dirt, debris, or water blowing out of the ground
- Liquids bubbling up from the ground or in water
- Distinctive, unusually strong odor of rotten eggs, mercaptan, skunk, or petroleum
- Discolored or dead vegetation, or discolored snow above a pipeline right-of-way
- Oil slick or sheen on flowing or standing water
- An area of frozen ground in summer, or an unusual area of melted snow in winter
Response Actions
General
- Safety first. Approach from upwind, uphill, and upstream with air-monitoring equipment for explosive and toxic levels.
- Wear proper PPE. Be prepared for flash fire. Use shielding for possible explosion. Use respiratory protection.
- Never operate pipeline valves (except in coordination with the operator). Uncoordinated closure can make the incident worse.
- Never attempt to extinguish a pipeline fire before the supply is shut off. Doing so can create a large flammable or explosive vapor cloud or liquid pool.
- Do not walk or drive into a vapor cloud to try to identify the product.
- Do not park over manholes or storm drains.
- Do not approach the scene with vehicles or mechanical equipment until isolation zones are established — vehicles are ignition sources.
- Secure the site and determine a plan to evacuate or shelter-in-place.
- Identify the product and operator. Look for pipeline markers with product, operator, and 24-hour emergency contact information.
- Notify the pipeline operator using the marker's emergency contact. The operator is a critical response resource.
- Establish a command post. Implement Incident Command Structure and prepare for Unified Command as stakeholders arrive.
Other Considerations
- If no flames are present, do not introduce ignition sources: open flames, running vehicles, or electrical equipment (cell phones, pagers, radios, lights, garage-door openers, fans, door bells).
- Abandon any equipment used in or near the release area.
- If safe, move far enough from the noise to allow for normal conversation.
- Pipelines often run near other utilities, railroads, and highways — all can be impacted or serve as ignition sources.
- Natural gas can migrate underground from the source through sewers, water lines, and geologic formations.
Establishing Protective Action Distances
Consider all of the following:
- Type of product
- If material is known, look up the 3-digit ERG guide via the blue (name) or yellow (UN) index — [ERG Guide Lookup →](/hazmat/guide)
- Pressure and diameter of the pipe (ask the operator)
- Time to valve closure (automated valves close quickly; manual valves take longer)
- Time for the product to dissipate after valves are closed
- Ability to conduct air monitoring / atmospheric sampling
- Weather (especially wind direction)
- Local variables: topography, population density, demographics, fire suppression available
- Nearby building construction material and density
- Natural and man-made barriers (highways, railroads, rivers)
Resources
United States
- National Pipeline Mapping System (NPMS). General locations of hazardous liquids and natural gas transmission pipelines within 500 ft of actual location. Emergency responders may apply for a web viewer account with more detail than is public. Does not contain gathering / production or distribution lines. <https://www.npms.phmsa.dot.gov>
- U.S. DOT PHMSA — Pipeline Safety Awareness. <https://www.phmsa.dot.gov/safety-awareness/pipeline/safety-awareness-overview>
- Pipeline Emergency Responders Initiative (PERI). <https://www.phmsa.dot.gov/pipeline/peri/pipeline-emergency-responders-initiative-peri>
- Pipeline Association for Public Awareness. <https://www.pipelineawareness.org/>
Canada
- Canada Energy Regulator (CER). <https://www.cer-rec.gc.ca/en/index.html>
One-Call ("Call Before You Dig")
- United States — 811 — routes to the appropriate state one-call center for damage prevention.
- Canada — Click Before You Dig — <https://clickbeforeyoudig.com/>