From an API document number to a defensible engineering basis
API standards are widely used throughout petroleum, petrochemical, LNG, chemical, and related process facilities. The practical challenge is rarely finding a standard number. The harder question is determining how the standard applies to the actual material, equipment, operating conditions, failure scenario, occupancy, or hazardous location being evaluated. HazBasis connects the standards framework to the project specific technical
Need help applying API standards to a real project? Reach out and we’ll help.
Find the API standard by the engineering question
| Engineering question | API direction | Related HazBasis path |
|---|---|---|
| How should a pressure relief device be sized and selected? | API 520 Part I; API 521 for scenario and system considerations | Pressure Relief System Design; VSP / DIERS testing where reactive systems are involved |
| Is the relief device installation likely to compromise performance? | API 520 Part II; related piping and installation requirements | Pressure Relief System Design / relief system review |
| What overpressure and depressuring scenarios need to be considered? | API 521 | Pressure Relief System Design; PHA / HAZOP / LOPA |
| How should a petroleum facility classify Class I Division hazardous locations? | API RP 500, coordinated with NEC / NFPA requirements | Hazardous Area Classification – NFPA / NEC |
| How should a petroleum facility classify Class I Zone hazardous locations? | API RP 505, coordinated with NEC / IEC project basis | Hazardous Area Classification – IEC / Zone |
| Are permanent or portable occupied buildings appropriately located? | API RP 752 / RP 753; RP 756 for tents where applicable | Facility Siting; QRA / consequence modeling |
| How should an atmospheric or low pressure storage tank be vented? | API 2000 | Flammable Liquid Fire & Explosion Analysis; engineering review |
| How should process safety performance be measured and trended? | API RP 754 | PSM program support; incident investigation / lessons learned |
Core API standards relevant to HazBasis process safety work
The following is a focused technical map, not an exhaustive API catalog. The correct standard set depends on the facility, equipment, jurisdiction, contract basis, and project scope.
Pressure Relief & Depressuring
API 520 Part I — Sizing and Selection of Pressure Relieving Devices
A primary reference for sizing and selecting pressure relieving devices in refinery and related process applications.
API 520 Part II — Installation
Addresses installation considerations that can materially affect pressure relief device performance and system reliability.
API 521 — Pressure Relieving and Depressuring Systems
Connects credible overpressure scenarios, relief system design, depressuring, disposal, and broader system-level considerations.
API 526 / API RP 576
Useful companion documents for pressure relief valve dimensions / selection interfaces and inspection of pressure relieving devices.
Related HazBasis services
Pressure Relief System Design | Chemical Reaction Hazard Analysis | VSP / DIERS Testing | PHA / HAZOP / LOPA
Hazardous Area Classification
API RP 500 — Class I, Division 1 / Division 2
Provides petroleum facility guidance for classifying locations where flammable gases or vapors may create hazardous electrical locations under the Division system.
API RP 505 — Class I, Zone 0 / Zone 1 / Zone 2
Provides Zone-based classification guidance for petroleum facilities and can be relevant when a project uses a Zone methodology.
Related HazBasis services
Hazardous Area Classification – NFPA / NEC | Hazardous Area Classification – IEC | Ignition Source Analysis | Flammable Gas / Vapor Hazard Analysis
Facility Siting & Occupied Buildings
API RP 752 addresses permanent buildings; API RP 753 addresses portable buildings; API RP 756 addresses tents. These documents support decisions about personnel exposure to explosion, fire, and toxic release hazards from nearby process units.
Related HazBasis services
Facility Siting | Quantitative Risk Assessment (QRA) | Consequence Modeling | Occupancy Analysis
Storage Tanks, Venting & Process Safety Management
API 2000 addresses venting of atmospheric and low pressure storage tanks. Other API documents may become relevant to overfill prevention, tank integrity, inspection, static / ignition control, and process safety performance depending on the project. API RP 754 provides a framework for process safety performance indicators in refining and petrochemical operations.
How HazBasis supports API-based engineering decisions
| Project step | HazBasis contribution |
|---|---|
| 1. Define the governing basis | Identify the applicable API document together with OSHA, NFPA, ASME, owner standards, jurisdictional requirements, and project specifications. |
| 2. Define credible scenarios | Establish fire, blocked outlet, utility failure, runaway reaction, vapor generation, loss of containment, explosion, toxic release, occupancy, or ignition scenarios as applicable. |
| 3. Generate or validate data | Determine whether laboratory data, physical properties, reaction calorimetry, VSP / DIERS data, flammability data, or other inputs are needed. |
| 4. Perform engineering analysis | Complete calculations, consequence modeling, hazardous area classification, facility siting evaluation, or structured hazard analysis. |
| 5. Document the decision basis | Provide assumptions, results, limitations, and recommendations clearly enough for engineering review and implementation. |
FAQ
Does HazBasis provide copies of API standards?
No. HazBasis explains practical application and engineering relationships. The official API publication and the project-specific adopted edition remain the reference of record.
Which edition of an API standard should my project use?
The applicable edition can depend on contract requirements, owner standards, regulatory incorporation, project date, jurisdiction, and AHJ expectations. Verify the project basis before design or compliance decisions are finalized.
Is API 520 the same as API 521?
No. They work together but address different aspects of pressure relief engineering. API 520 focuses on pressure relieving devices and their sizing / selection / installation, while API 521 addresses broader pressure relieving and depressuring systems and scenario considerations.
Can HazBasis review an existing pressure relief calculation?
Yes, when within project scope. A review can examine scenario selection, input data, assumptions, sizing basis, reactive-system considerations, and the connection between relief-device sizing and the overall relief / disposal system.
Can API RP 500 or RP 505 replace a full hazardous area study?
A standard provides methodology and guidance; a project still needs material data, release sources, ventilation, equipment conditions, drawings, and an engineering classification basis appropriate to the facility.