Glossary

  • Active Ventilation - intentional movement of air using fans, blowers or other mechanical devices. Also called mechanical or forced ventilation.
  • Administrative Controls - procedures or rules that are to be followed to reduce the risks associated with a hazard for which engineering controls are not practical or possible. Although administrative controls can (and should) always be used to control employee exposure, they are prone to human error and cannot be relied upon to reduce exposure all the time. Examples of administrative controls include policies restricting access and signage.
  • Authority Having Jurisdiction - an organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.
  • Bayonet Joint - a high-performance joint, called the bayonet joint, originally developed by Dr. Herrick L. Johnston (J.C. Daunt and H.L.Johnston (1949). Rev. Sci. Instr., v.20, pg.122), is used for lines that must be dismantled frequently or for applications in which a low heat inleak at the joint is required. The bayonet joint consists of a male portion that telescopes within the female portion. The clearance between the male and female portions is made such that no liquid can flow into the space, and gaseous convection is suppressed.
  • Bellow - the flexible element of an expansion joint consisting of one or more convolutions and the end tangents, if any.
  • Best Practice - a technique or methodology that has reliably led to a desired result
  • Blast Wave - a shock wave in air, caused by the detonation of explosive material
  • Buddy System - A system of organizing employees into work groups in such a manner that each employee of the work group is designated to be observed by at least one other employee in the work group. The purpose of the buddy system is to provide rapid assistance to employees in the event of an emergency. It is important that the employee designated as observer not be subject to hazards in the work area.
  • Buoyancy - the tendency of a gas to rise in air
  • Change Control - process or procedure to manage changes being made, including the submission, analysis, decision-making, approval, and implementation of the change. Uncontrolled changes are one of the most common causes of project failure.
  • Charpy Impact Test - a destructive test of impact resistance, consisting of placing the specimen in a horizontal position between two supports, then applying blows of known and increasing magnitude until the specimen breaks
  • Chronic Maintenance - the need for frequent, repeated maintenance on a piece of equipment
  • Compressed Hydrogen Gas - hydrogen compressed to a high pressure and stored at ambient temperature
  • Consequence - the extent to which an event causes injury or damage.
  • Cryogenic Liquid - a liquid with a boiling point below -150° C (-238° F). Note that liquid hydrogen is at -423° F
  • Deflagration - a flame moving through a flammable mixture
  • Detonation - an exothermic chemical reaction coupled to a shock wave that propagates through a mixture of fuel and oxidizer
  • Dewar - a non-pressurized vacuum-jacketed container used to hold cryogenic liquids
  • Diffusion in Air - gradual mixing of gas molecules in air due to random thermal motion
  • Energy Isolating Device - a mechanical device that physically prevents transmission or release of energy (e.g., a control valve)
  • Engineering Controls - controls designed to eliminate or reduce exposure to a hazard through the use or substitution of engineered machinery or equipment. Examples of engineering controls include ventilation systems (fume hoods), sound-dampening materials to reduce noise levels, and safety interlocks.
  • Expansion Joint - any device containing one or more bellows used to absorb dimensional changes, such as those caused by thermal expansion or contraction of a pipeline, duct, or vessel
  • Fail Safe Designs - any failures will leave a system in a condition that will be safest for personnel and will cause the least amount of property damage.
  • Fit for Maintenance - Piping and equipment in hydrogen service should be purged with an inert gas prior to being taken offline for maintenance. Cryogenic vessels should be drained and warmed to ambient temperature.
  • Flameout - accidental extinguishment of a pilot flame on a flare system
  • Formalized Hydrogen Training Plan - a formalized hydrogen training plan may include: 1) pressure safety, 2) cryogenic system safety, and 3) electrical worker training. The formalized training plan should require that classes are updated and personnel are re-certified periodically.
  • Hazard - an object or situation that is potentially dangerous (i.e., an unsecured electrical cord might be a tripping hazard, or a finger-tight connection that is not in a properly vented area might start to leak into an enclosed space, leading to a flammable accumulation of hydrogen)
  • Hot Work - work involving electric or gas welding, cutting, brazing, or similar flame- or spark-producing operations
  • Hydrogen Embrittlement - the ability of hydrogen to cause significant deterioration in the mechanical properties of metal
  • Incident - an event that results in:
    • a lost-time accident and/or injury to personnel
    • damage to project equipment, facilities or property
    • impact to the public or environment
    • an emergency response or should have resulted in an emergency response
  • Inherent Safety Features - system design such that in both normal and emergency situations at least two failures must occur before injury, loss of life, or major equipment damage would result from the use of hazardous materials
  • Likelihood - the chance that an event might happen
  • Lockout - placement of a lock on an energy isolating device
  • Management of Change (MOC) - a formal process for systematically managing variances and changes to materials, technology, equipment, procedures, personnel and facility operation for their effect on safety vulnerabilities
  • Maximum Allowable Working Pressure (MAWP) - the maximum gauge pressure permissable in a pressure vessel
  • Mean Time Between Failures (MTBF) - average calendar time from the onset of one failure to the onset of the next, including time to repair
  • Near-Miss - an event that, under slightly different circumstances, could have become an incident. Examples include:
    • any unintentional hydrogen release that ignites, or is sufficient to sustain a flame if ignited, and does not fit the definition for an incident
    • any hydrogen release which accumulates above 25% of the lower flammability limits within an enclosed space and does not fit the definition of an incident
  • Operating Procedure - an established sequence of steps to be followed when operating a piece of equipment or a system
  • Overpressure - the pressure in a blast wave above atmospheric pressure
  • Oxidant - a chemical reagent that oxidizes another material (e.g., causes combustion of a fuel to occur)
  • Passive Ventilation - process by which the air in a room or building is supplied or removed by natural means (no mechanical devices). Passive (or natural) ventilation is effective because it takes advantage of buoyancy effects due to temperature or composition differences.
  • Personal Protective Equipment (PPE) - clothing and/or equipment designed to protect workers from workplace injuries (e.g., face shields, safety glasses, hard hats, safety shoes, goggles, coveralls, gloves, vests, earplugs, respirators)
  • Predictive Maintenance - an approach that determines when maintenance is needed based on the actual equipment condition and data on past performance
  • Pressure-Relief Device (PRD) - a safety device installed on tanks, pipes, and component systems to prevent damage due to overpressure
  • Preventive Maintenance - any planned maintenance designed to extend equipment life and avoid unscheduled maintenance outages. The goal is to prevent equipment failure rather than react to it.
  • Reactive Maintenance - the practice of waiting until an equipment failure occurs and then repairing the equipment
  • Reliability-Centered Maintenance - a systematic approach to evaluate a facility's equipment and develop a cost-effective approach to maintaining its reliability, by focusing attention on the higher-priority components first
  • Risk - the statisical chance of danger from an event; an evaluation of the severity and likelihood of an event
  • Safety Authority - a person or group of people recognized as safety experts in a particular field. The safety authority may be personnel appointed by your institution (e.g., a hydrogen safety committee) or they may be external consultants hired to review your safety plans.
  • Safety Culture - The assembly of characteristics and attitudes in organizations and individuals that establishes, as an overriding priority, that safety issues receive the attention warranted by their significance. It is the product of workers, managers, institutional values, attitudes, perceptions, competencies, and patterns of behavior that determine the commitment to, and the proficiency of, an organization's health and safety management.
  • Scheduling - deciding when the job will be done and which trained personnel will do it
  • Scope of Work - a series of actions or directions that accomplish a particular goal
  • Severity - the extent to which an event causes injury or damage
  • Standard Operating Procedure - an established sequence of steps to be followed when operating a piece of equipment or a system
  • Stop Work - provides workers the right, without reprisal, to decline to perform an assigned task because of a reasonable belief that the task poses an imminent danger or other hazard, coupled with a reasonable belief that there is insufficient time to seek effective redress through the normal reporting and abatement process. Establishes the authority and responsibility for workers to stop work when they discover that employees are exposed to conditions of imminent danger or to other hazards.
  • Stressors - parameters outside the design envelope (e.g., vibrations, friction, misalignment)
  • Subject Matter Expert - a group of Subject Matter Experts for work involving hydrogen may include: fire marshal, fire protection engineer, pressure safety engineer, explosive safety engineer, plant engineer, air quality engineer, electrical safety engineer, industrial hygienist, and ES&H coordinator
  • Tagout - placement of a prominent warning device (e.g., a tag) on an energy isolating device
  • Tangent - the straight unconvoluted portions at the end of the bellows
  • Tube Trailer - In the U.S., a truck-trailer chassis designed to transport large horizontal tubes of compressed hydrogen gas. In Europe, tube trailers can be designed for vertical cylinders.
  • Ullage Volume - space between the liquid level and the top of the vessel