National Safety Council
Compiled by
Dr. S.D. Allen Iske, Associate Professor
University of Central Missouri

• Boiler: A closed vessel in which water is heated by combustion of fuels or heat from other sources.

• Unfired pressure vessels: air tanks, steam-jacketed kettles, digesters, vulcanizers, and other such vessels

• High-temperature water: Water kept in closed systems under a high pressure so that it remains a liquid rather than turning into steam.
• Pressure parts: Any component of a vessel, boiler, or water heater that retains steam, hot water, or other fluids under pressure.
• ASME: American Society of Mechanical Engineers
• NBIC: National Board of Boiler and Pressure Vessel
Inspector’s Code

• Boilers and unfired pressure vessels
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• Found in workplaces —offices, hospitals, manufacturing plants, hotels, garages, warehouses
Contents within vessels —gases, vapors, liquids, solids
• Toxic and benign substances
• Pressures ranging from almost full vacuum to thousands of psi
• Temperatures ranging from hundreds of degrees below zero to well over 1000 °F

• Fires
• Burns
• Explosions
• Asbestos

BLEVE: boiling liquid expanding vapor explosion
This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous.
A BLEVE results from the rupture of a vessel containing a liquid substantially above its atmospheric boiling point. The substance is stored partly in liquid form, with a gaseous vapor above the liquid filling the remainder of the container.
Image source: Wikipedia, 2009

• Boilers and high-temperature water heaters
• Pressure part ruptures
• Furnace explosions
• Unfired pressure vessels
• Pressure part ruptures

• Four elements for compliance with ASME
• design
• fabrication
• testing
• installation

• ASME Boiler and Pressure Vessel Code
• National Board of Boiler and Pressure Vessel Inspectors
Code —governs inspection, repair, and alteration of boilers and pressure vessels after placed in service
• Boilers and pressure vessel operations are strictly regulated within jurisdiction of states, municipalities, or
Canadian provinces.
• Synopses of boiler and pressure vessel laws, rules, and regulations are available from Uniform Boiler and
Pressure Vessel Laws Society.
• National Fire Protection Associations Boiler-Furnace
Standards (NFPA 85A –85E)

• Compliance with ASME is authorized by inspectors commissioned by the National Board of Boiler & Pressure
Vessel Inspectors —licensed by state or provincial governmental authority charged with enforcement.
• installation
• operation
• inspection
• repairs and alterations
• routine safety checks

• I Rules for Construction of Power Boilers
• II Material Specifications
• III Nuclear Power Facility Components
• IV Rules for Construction of Heating Boilers
• V Nondestructive Examination
• VI Recommended Rules for Care and Operation of
Heating Boilers
• VII Recommended Rules for Care of Power Boilers

• VIII Rules of Construction for Pressure Vessels
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Division 1
Division 2 —Alternate rules
Division 3 —Alternate rules
• IX Welding and Brazing Qualifications
• X Fiberglass-Reinforced Plastic Pressure Vessels
• XI Rules for In-service Inspection of Nuclear Power Plant
Components

• ASME Code —covers design, fabrication, and inspection requirements only during construction of boilers and pressure vessels
• NBIC Code —standard governs after initial installation of boiler or pressure vessels
• NBIC —guidelines for inspection, repair, alteration, rating, and rerating for the remainder of boiler or pressure vessel’s service life
• Manufacturer’s instructions—installation and maintenance

• Train operating personnel:
• to operate equipment properly
• to make routine safety checks
• to call qualified maintenance personnel if necessary or appropriate
• National Board
• Certificates of authorization to perform specific tasks
• NB stamps

• Errors in design, construction, and installation
• Improper installation, human failure, and inadequate training of operators
• Corrosion/erosion of construction materials
• Failure or intentional defeat of safety devices; failure or override of automatic control devices
• Failure to inspect and test thoroughly, properly, and frequently
• Improper application of equipment; overfiring
• Lack of planned preventive maintenance

• Explosion hazards
• Fire hazards —leakage of fuel or gas

• Fully enclosed boiler rooms
• Large door openings on boiler rooms
• Noncombustible ceiling and automatic sprinklers
• Proper clearance around exterior walls

• Establish testing and servicing program.
• Always test safety and relief valves under pressure.
• Have repairs made immediately.
• Check and service the boiler in and out of heating season.
• Keep a boiler log.

• Boiler —a closed vessel in which water is heated and steam is generated or superheated under pressure by the direct application of heat
• Heat sources —combustion of fuel, most common; also electricity and waste heat from chemical reaction
• Boilers —firetube or watertube
• Boilers registered and certified in accordance with state or local agencies. Some states require operators to be licensed.

• Controls and instrumentation —monitor and control combustion and steam production
• Economizers —transfer heat from flue gas to incoming feed water
• Super heaters —increase temperature of steam
• Air repeaters —transfer heat from flue gas to incoming air
• Chimneys —discharge products of combustions
• Ash-disposal equipment —remove ash produced

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Water treatment —remove dissolved O
2 pH and CO
2
, control
Blow down pipes and valves —remove sludge and impurities in boiler water
Safety valves and fusible plugs —safe operation, relieve excess pressure or vacuum conditions
Steam pressure and water-level indicators/controls — monitor safe and proper operation
Good piping practice —minimize maintenance work and easy to reach
Placing boilers in and out of service —manufacturer’s recommendations

• Clean boilers promptly.
• Follow correct guidelines.
• Schedule maintenance guidelines.
• Follow general precautions for entrance.
• Wear proper attire when entering.

• Safety precautions:
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• floors —slippery and dirty lighting —source of emergency lighting; controls and gauges well lit; spare flashlights; exits well lit and identified exits —two or more exits (remotely located from each other); proper exits for each story to a fire escape or directly outside
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• emergency shutdown buttons at exits stairs, ladders and runways —proper access to operate and service boiler safely

• Operator error is a major contributing factor in boiler accidents.
• Operators must understand the process and hazards with the system, including the purpose and principles of the control and safety devices installed.
• Procedures for start-up, shutdown and basic troubleshooting must be developed with assistance from the manufacturer or a qualified person. Emergency procedure must be developed for operation.
• Train multiple operators as well as security personnel patrolling premises and facility.

• High-temperature water (HTW) vs. steam and cold water —break in pipe/equipment
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• HTW release —volume increases at high rate, energy released at very low rate; no energy for rupturing equipment or imparting energy to fragments, but high potential for scalding injuries
Steam and cold water release —16 times more energy released during expansion than HTW escape; energy left to produce explosive effect
• Main causes of failure
• operating errors or mechanical forces (water hammer, thermal expansion and thermal shock)
• faulty materials

• Vessels designed to contain fluids under internal pressure or vacuum and not heated directly through the combustion of fuels or other external heat sources.
• Found in commercial and industrial facilities.
• Heat can be generated from chemical reactions within vessel or by applying a heating medium within the vessel or circulating it around the vessel (jacket).
• Examples: compressed air tanks, propane tanks, deaerators and condensate tanks, steam-jacketed kettles, pulp mill digesters, rubber vulcanizers

• ASME Code UPV exceptions:
• vessels subject to federal regulations
• vessels with a nominal capacity of 120 gal (450 l) or less of water under pressure, in which any trapped air serves only as a cushion
• vessels having an internal or external operating pressure not exceeding 15 psi (103 kPa), with no limitation on size
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• vessels with an inside diameter not exceeding 6 in. (15 cm), and no limitation on pressure hot-water storage tanks heated by steam or other indirect means — heat input of 200,000 Btu (59,000 J/s) or less, water temperature of
200ºF (93ºC) or less, and nominal capacity of 120 gal (450 l) or less

• Design: ASME Code, Section VIII
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• Division I —normally covers vessels with ratings of 3,000 psi or less.
Division II —normally covers vessels used at pressures exceeding
3,000 psi.
Other Codes —American Petroleum Institute’s code or state and local codes may be enforced. Codes may impose size or service limits more restrictive than ASME Code.
• Secondhand vessels
• Prior to purchase, written report that equipment meets requirements of jurisdiction where it is to be installed.
• Have the equipment inspected by a NB licensed inspector.

• Internal inspection
• Periodic internal inspections to evaluate integrity of equipment.
• Inspections should be carried out by NB licensed inspectors to ensure compliance with jurisdictional or insurance requirements.
• Preventive maintenance

• Inspection or maintenance department should keep file or log of original design documents, records of inspections, and vessel history documents.
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• blueprints manufacturer’s data reports and instructions
• design data, including location of dimensional checkpoints
• installation information
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• records of process changes vessel’s historical profile, including records of all repairs and conditions found during inspections

• Develop safe policy and procedure for entering tanks
• Confined space with permit and lockout/tagout safety procedures required by OSHA
• Potential hazards of confined spaces:
• toxic materials including inert gases
• flammable vapors which may be ignited
• insufficient oxygen
• heat or smoke from fire inside vessel
• introduction of hot gases or fluids from external sources
• start up of agitators or putting confined space in motion

• Prior to entry into pressure vessel:
• Ensure it is properly drained, ventilated, and cleaned
• Test atmosphere for oxygen content, explosiveness, and toxic levels
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Disconnect and blank all connecting pipelines, or close, lock out, and tag valves on the line
All power-driven devices —disconnected, locked out, and tagged
• Confined-space permit issued
• Provide access for safe entry and exit from vessel
• Use safety harnesses and lifelines
• Put on proper PPE

• Clean and purge the vessel’s internal surfaces prior to entry.
• Use specific methods based on the substance contained inside the vessel.
• Forced ventilation is required to ensure all potentially harmful or dangerous gases and vapors have been removed.
• Test atmosphere prior to entry as well as routinely throughout work processes inside a vessel.

• Hydrostatic tests
• Can be used for vessels constructed without access for an internal inspection to ensure the vessel is fit for continued service.
• Targeted for the maximum allowable working pressure, the set pressure of the lowest installed safety valve, or the normal operating pressure of the boiler or pressure vessel at discretion of the authorized inspector.
• Testing should follow ASME Code and NBIC Codes.
• Minimize hazards to personnel during testing, isolate test area from operations, and provide suitable barricades.

• Detecting cracks/measuring thickness
• Ammonia released inside vessel and compressed air applied to a maximum pressure 50% of working pressure is obtained; swab soaked in hydrochloric acid passed over all seams and suspect areas; presence of white vapor (ammonium chloride) indicates leakage
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Burning sulfur stick
Non-destructive methods (NDE) —radiography (RT) and ultrasonic examination (UT) —detect cracks, wastage, and other adverse conditions
Lacquer method —apply lacquer to clean system, then conduct hydrostatic test, and examine for cracking of lacquer

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Thoroughly train employees working with pressure vessels in routine duties and emergency procedures.
Supervisors should be qualified and knowledgeable.
Review potential hazards of processes and systems.
Written detailed procedures should be reviewed periodically and made available to personnel.
Use a checklist in the training process for start-up, shutdown, or routine processing cycle.
Communication between all staff and personnel is critical.
Proper labeling of valves, piping systems, and control equipment prevents accidents caused by operator error.

• UFP vessels used in processes with various materials and chemicals, equip each vessel with appropriate safety devices for the type of vessel and work performed.
• Safety devices are installed for a purpose:
• protect against overpressure
• chemical reactions
• abnormal conditions

• Types of safety devices:
• safety valves
• rupture disks
• vacuum breakers
• water seal
• vents
• regulating or reducing valves

• Pressure interlocks should be installed on autoclaves and other pressure vessels containing large volumes of steam equipped with quick-open doors or reclosing devices.
• Pressure interlock will prevent the opening of the door until all pressure is relieved and prevent introduction of steam until the door is closed.
• Opening the door with chamber under pressure will release extreme force and may cause accidents. Interior items may be released like projectiles.
• Most critical system of these vessels is the closure system and its components.
• Operators routinely inspect as well as licensed inspectors.

• Specific pressure vessel safety procedures:
• Do not weld to any part of the vessel.
• Do not cut, drill, or fasten to any part of the vessel.
• Assume vessel is pressurized any time the door is closed.
• Check for sufficient oxygen.
• Leave no flammable materials, debris, or plastics in autoclave.
• Closure alignment/inspect vessel
• Schedule periodic maintenance.

• Used to heat liquid mixtures to moderate temperature
• Steam circulated between the outer and inner shells of vessel and heat transferred through the inner shell to the contents of vessel
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• Use safety valves
• Operating procedures for safety:
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Thoroughly drain the steam space prior to adding steam to jacket.
Admit steam to cold vessels slowly to allow for parts to heat and expand uniformly.
Unless automatic protection, open vents only when steam is shut off.
Where agitators are used, paddles must not strike the interior surfaces of the vessel.
Vessels with large openings must have adequate safety measures to prevent falls by personnel into the vessel.
Fill only to the point where specified and do not create undue splashing.

• Shallow pans containing steam coils
• Operational rules to avoid accidents:
• Attend to the pans continuously during operation.
• After each use, thoroughly clean the pans and coils.
• After shutting off steam in the coils, drain them to prevent the product from being drawn into lines when steam condenses and creates a vacuum. Installing a vacuum breaker would also prevent this.

• Hazards of high-pressure systems result from failures due to leaks, pulsation, vibration, and overpressure.
• Injuries are possible to employees from the high-pressure release of steam or gas as well as projectiles thrown from ruptures or unrestrained sections of piping, tubing, or hoses.
• Potential for injury and damage is very high.

• Pressure gauges used at 1800 psi or more should have these properties:
• full size
• blowout backs
• integral sides
• front designed to withstand internal explosion
• have multi-ply plastic or double-laminated safety glass cover for gauge faces
• install substantial shield in front of high-pressure gauges