API RP 753:2007 pdf download

API RP 753:2007 pdf download.Management of Hazards Associated with Location of Process Plant Portable Buildings.
Portable buildings or shelters occupied only for short duration (e.g., portable toilet facilities, smoking shelters, weather shelters) should be evaluated on a case-by-case basis.
2.3 PORTABLE BUILDINGS NOT INTENDED FOR OCCUPANCY
Portable buildings not intended for occupancy do not need to be sited for explosion, fire, or toxic release hazards. Controls should he implemented to ensure that the use of these portable buildings does not change to “portable buildings intended for occupancy”. Personnel, however, may periodically be present in these portable buildings to perform their duties.
The following examples are portable buildings and structures that are generally not intended for occupancy:
• Tool trailers or storage sheds without attendant stationed inside
• Decontamination facilities
• Control equipment enclosures
• Analyzer sheds
• Portable electrical substations
• Portable electric generators
2.4 OTHER OCCUPIED PORTABLE STRUCTURES
This section addresses a group of portable structures that are used to support temporary work activities within covered process areas and are often mandated by regulatory requirements. Current technology is typically not sufficient to provide the capability to remotely perform these activities. The siting evaluation described in this document does not apply to these structures. Examples include:
• Mobile environmental monitoring stations
• Supplied air trailers
• Inert entry life support trailers
• Vehicles housing equipment stations (e. g., trucks or vans with X-ray equipment)
Special characteristics of these structures include:
• Required to be located inside or near the process unit. (For example, due to physical connections between equipment in the portable building and the unit equipment)
• Support essential activities to ensure personnel safety, necessary maintenance or environmental monitoring and testing
• Present only for the duration of the specitic activity and removed immediately thereafter
• Maneuverable for placement in congested areas for access to nested equipment and stacks
• Accommodate low numbers of personnel
Risk mitigation measures for these structures shall include:
• Direct communications of occupants with operations
• Authorized work permit for their temporary presence
• Awareness training of process unit hazards for occupants
• Emergency response and evacuation procedures
• Minimized occupancy, which includes controls to confirm that personnel not directly involved in a critical ongoing activity (e. g., start-up and planned shut-down) are evacuated from these portable structures
This recommended practice does not apply to portable structures that are not buildings. Examples include:
• Welding enclosures
• Asbestos or refractory remediation enclosures
• Cranes or other equipment with operator cabins
For congested volumes less than 7,500 cubic ft, portable buildings intended for occupancy shall be located at a standoff distance greater than 330 ft or at a distance determined by performing a Detailed Analysis.
For congested volumes greater than 1,000,000 cubic ft a Detailed Analysis is required. Further, the Zone 1 guidance in Table I applies and the Zone 1 standoff distance for light wood trailers shall not be less than 570 ft.
The use of portable buildings in Zone I that have facilities that could be used for meetings shall be controlled such that they are used only by essential personnel.
3.1 SIMPLIFIED METHOD
The Simplified Method recommends placement of portable buildings intended for occupancy oniy in Zone 3. Standoff distances to Zone 3 in Figure 1 are determined by calculating congested volumes as described in Appendix B. Portable buildings located in Zone 3 are expected to retain structural integrity but may sustain window breakage. Mitigation of potential window hazards should be considered. The additional risk reduction recommendations in Section 3.5 should be considered.
3.2 DETAILED ANALYSIS
A Detailed Analysis is required for siting any portable building in Zone 1 or Zone 2 of Figure 1. Methods include Consequence Analysis and Quantitative Risk Assessment (QRA) both of which are discussed below.
Personnel performing the detailed analysis shall have competence in the analytical procedures and the components of the analysis. Areas of competency shall include as appropriate the application of the methodology being employed, hazard identification, scenario development, flammable dispersion modeling, explosion modeling, blast response of structures, frequency assessment, and mathematical techniques.
3.2.1 Consequence Analysis
A Consequence Analysis is a detailed, technical assessment of potential consequences from explosion hazards, and includes the prediction of blast loads and the estimation of potential damage to defined portable buildings. Consequence Analyses should be based on major release scenarios, considering incidents and their outcomes that have or could have occurred in similar process units within industry (i.e., scenarios with the most severe consequences).
The estimation of Vapor Cloud Explosion blast loading should include but is not limited to:
• Flammable cloud size
• Fuel reactivity
• Process area congestion
• Congested volume
• Confinement
• Explosion severity or flame speed
• Separation distance between adjacent congested volumes
• Distance between the hazardous process area and the portable building The following additional explosion hazards may require additional or different considerations.
• Condensed phase chemical explosion
• Dust explosion
• Boiling Liquid Expanding Vapor Explosions (BLEVEs)
• Vapor cloud explosions at enclosed process units
• Pressure vessel burst
• Runaway chemical reactions.