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API Publ 2013-1991: Safety Procedures for Cleaning Mobile Tanks in Service
Scope, Technical Requirements, and Compliance Notes for the 1991 Edition
API Publ 2013-1991 (often referred to as the 1991 edition of API Publication 2013) provides guidelines for the safe cleaning of mobile tanks—including tank trucks, rail tank cars, and portable tanks—that transport flammable or combustible liquids, such as petroleum products and chemicals. This article summarizes the key elements of the publication, focusing on its scope, technical requirements, implementation highlights, and compliance notes.
Scope and Application
API Publ 2013-1991 applies to cleaning operations performed on tanks that have been in service with Class I (flammable) or Class II/III (combustible) liquids. The standard covers three main phases:
- Preparation for cleaning – including product removal, isolation, and vapor elimination.
- Cleaning operations – mechanical, chemical, or steam cleaning methods.
- Return to service – inspection, drying, and re‑certification.
The publication excludes permanently installed process vessels and storage tanks, focusing strictly on mobile vessels that are frequently emptied and re‑filled. It emphasizes the critical need to eliminate flammable atmospheres before any personnel entry or hot work.
Applicability by Tank Type
| Tank Type | Examples | Typical Products |
|---|---|---|
| Tank trucks | Road tankers, ISO tanks on trucks | Gasoline, diesel, ethanol, chemicals |
| Rail tank cars | Pressured and non‑pressurized rail cars | Crude oil, LPG, liquid chemicals |
| Portable tanks | IBCs, drums, totes | Solvents, industrial oils, hazardous materials |
Technical Requirements
API Publ 2013-1991 establishes a structured set of technical requirements to ensure the safety of personnel and equipment. These are divided into three key areas:
1. Pre‑Cleaning Assessment and Isolation
Before cleaning, the tank must be emptied of residual product and isolated from all sources of flammable or reactive material. Requirements include:
- Lockout/tagout of all product lines, vent lines, and heating coils.
- Grounding and bonding to prevent static ignition during product transfer.
- Identification of the Last Product Carried (LPC) to select appropriate cleaning solvents and PPE.
2. Atmosphere Control and Testing
The standard specifies that before personnel entry or hot work, the tank atmosphere must meet the following threshold limits:
| Parameter | Permissible Limit |
|---|---|
| Flammable vapor (as % LFL) | ≤ 10% of Lower Flammability Limit |
| Oxygen content | 19.5% – 23.5% (by volume) |
| Toxic contaminants (e.g., benzene, H₂S) | Below OSHA PEL / ACGIH TLV |
Vapor removal is typically accomplished by ventilation (natural or forced), steam cleaning, or inert gas purging (e.g., nitrogen). If inerting is used, oxygen must be maintained below 8% for hot work, but personnel shall not enter an inerted tank unless breathing air and positive‑pressure PPE are provided.
3. Personal Protective Equipment (PPE) and Personnel Training
The publication requires:
- Minimum PPE: chemical‑resistant gloves, splash‑proof goggles, and flame‑resistant coveralls.
- For confined space entry (tanks of limited opening), additional PPE is mandatory: respirators, harnesses, and lifelines.
- All workers must be trained in confined space procedures, emergency evacuation, and the proper use of gas monitors.
WARNING: Never enter a tank that has been inerted with nitrogen or another asphyxiant without supplied‑air respiratory protection. The 1991 edition strongly prohibits entry into any tank with an oxygen concentration below 19.5%.
Source: API Publ 2013-1991, Section 4.3.
Source: API Publ 2013-1991, Section 4.3.
Implementation Highlights
Successful implementation of API Publ 2013-1991 requires attention to several practical details:
- Written Procedures: Each facility must develop site‑specific Standard Operating Procedures (SOPs) that incorporate the steps of the publication.
- Continuous Gas Monitoring: Use calibrated, multi‑gas detectors capable of reading LFL, O₂, CO, H₂S, and VOCs. Perform bump tests daily.
- Permit System: A formal confined space entry permit (similar to OSHA 29 CFR 1910.146) must be used for every tank entry.
- Emergency Rescue: Pre‑plan rescue drills; have retrieval equipment and trained standby personnel ready outside the tank.
Tip: When steam cleaning tanks that held hydrocarbons, collect and dispose of the condensate and sludge in accordance with local environmental regulations. The 1991 edition notes that some residuals may still be flammable after steam cleaning.
Success Story: A chemical terminal in Alabama adopted API Publ 2013-1991 as its baseline for cleaning tank trailers. Within its first year, the facility reduced confined space incidents by 80% and eliminated all hot‑work flash fires.
Danger: Never assume a tank is “gas‑free” based solely on its last cargo. Residual vapors in blind spots (e.g., baffles, sumps) can create explosive pockets. The standard mandates multiple test locations for every cleaning operation.
Compliance Notes
Compliance with API Publ 2013-1991 is generally voluntary under the API umbrella, but it is often referenced by regulatory bodies and insurance companies as an industry consensus standard. Even though the 1991 edition has been superseded by newer versions (e.g., API 2013 8th edition, 2020), the core safety principles remain valid and auditable. Key compliance considerations include:
- Regulatory Alignment: The publication aligns closely with OSHA’s Confined Space Entry standard and the EPA’s Spill Prevention, Control, and Countermeasure (SPCC) rules where cleaning involves transferring of oil.
- Record Keeping: Maintain records of gas monitoring results, training rosters, and entry permits for at least 3 years (or as required by authority having jurisdiction).
- Updating Procedures: Facilities should compare their existing SOPs against the latest edition of API 2013 to incorporate improvements in vapor detection, PPE, and rescue techniques.
Q: Does API Publ 2013-1991 apply only to tanks that have carried petroleum products?
A: No. While it primarily addresses flammable and combustible liquids associated with hydrocarbons, the standard also covers chemical loads (e.g., alcohols, ketones). The key is that the product presents a fire, explosion, or toxic hazard during cleaning.
A: No. While it primarily addresses flammable and combustible liquids associated with hydrocarbons, the standard also covers chemical loads (e.g., alcohols, ketones). The key is that the product presents a fire, explosion, or toxic hazard during cleaning.
Q: Can I use API Publ 2013-1991 for cleaning tanks that hold non‑flammable chemicals?
A: Yes, but you must also comply with any additional health or reactivity standards for that specific chemical. The 1991 edition provides a solid foundation for atmosphere control and confined space safety that applies to virtually any volatile compound.
A: Yes, but you must also comply with any additional health or reactivity standards for that specific chemical. The 1991 edition provides a solid foundation for atmosphere control and confined space safety that applies to virtually any volatile compound.
Q: Is the 1991 edition still considered valid for regulatory compliance?
A: Many authorities accept the 1991 edition as a recognized standard, but it is recommended to adopt the latest edition (currently API 2013, 8th edition, 2020) to take advantage of updated references and modern safety practices. If your company relies on the 1991 version, be sure to document any variances in your safety management system.
A: Many authorities accept the 1991 edition as a recognized standard, but it is recommended to adopt the latest edition (currently API 2013, 8th edition, 2020) to take advantage of updated references and modern safety practices. If your company relies on the 1991 version, be sure to document any variances in your safety management system.
This article is based on the 1991 edition of API Publication 2013 and is intended for informational purposes. Always consult the most current API standard for full compliance and refer to local regulations.