API TES key terms

An enclosed or partially enclosed area with limited entry and exit, not designed for continuous occupancy, where hazardous atmospheres or engulfment can occur. Cargo tanks qualify as confined spaces.

A written authorization completed before entry that records the space identity, hazards, isolation, test results, entry team, and controls. Entry may not begin until the permit is signed by the responsible person.

The competent person who authorizes entry, verifies that all controls and tests are in place, monitors the work, and orders evacuation when conditions change. This role is distinct from the standby person.

A trained crew member stationed at the entrance who maintains continuous communication with entrants, tracks who is inside, keeps the area clear, and summons help. The standby person does not enter to attempt rescue.

The agreed method and interval for contact between the standby person and those inside, such as voice, lifeline signals, or radio checks. Loss of communication is treated as an emergency.

Measuring oxygen content, flammable gas or vapor, and toxic gas levels with calibrated instruments before entry and at intervals during work. Results must be recorded, and testing is repeated whenever conditions may have changed.

The scheduled check of an instrument against a known reference gas so readings stay accurate. Bump tests before use and full calibrations at set intervals are normally required, with results logged.

An atmosphere with less than 19.5 percent oxygen by volume, which impairs judgment and can cause unconsciousness quickly. It may result from inerting, rusting, combustion, or displacement by other gases.

An atmosphere with more than about 23.5 percent oxygen, which makes materials burn far more readily and clothing or rags ignite easily. Enriched atmospheres must be ventilated before entry or hot work.

The lowest concentration of a gas or vapor in air that will support combustion. Entry or hot work is normally prohibited unless readings are well below this limit, often at or under one percent by volume.

The highest concentration of a gas or vapor in air that will burn. Above this limit the mixture is too rich to ignite, but dilution with air can bring it back into the flammable range.

The gas given off by a liquid such as petroleum cargo or solvent that can ignite when mixed with air in the right proportion. Vapors are often heavier than air and collect in low areas.

The weight of a vapor compared with an equal volume of air. Values above one mean the vapor is heavier than air and tends to settle in tank bottoms and bilges.

A gas such as nitrogen or cleaned flue gas with too little oxygen to support combustion, used to blanket cargo tanks and prevent explosions. An inerted space must never be entered without breathing apparatus.

Replacing the atmosphere in a tank with inert gas so the oxygen content falls below the level needed for combustion. It protects against explosion but creates a lethal atmosphere for people.

Displacing unwanted gas or vapor from a tank with air, inert gas, or another gas to reach a target atmosphere. Purging is done before cleaning, gas freeing, or hot work.

Removing toxic or flammable gas from a tank until the atmosphere is safe for entry without breathing apparatus. It is confirmed by testing and normally certified by a competent person.

Forcing or allowing fresh air through a tank to remove vapors and supply oxygen. Mechanical ventilation with the exhaust placed low is common because many cargo vapors are heavier than air.

Physically separating a tank from every energy and product source before entry, using blanked flanges, spades, or closed and locked valves. Isolation prevents cargo, steam, or inert gas from entering unexpectedly.

A procedure in which energy sources are switched off, locked, and marked with a warning tag held by the person doing the work. Only the person who applied the lock removes it.

Inserting a solid plate or spade between pipe flanges to stop flow into a tank, with the position recorded and the plate visible or tagged. It is a positive isolation method preferred over a single closed valve.

Trained personnel with breathing apparatus and rescue equipment who are ready to recover an incapacitated entrant. Untrained coworkers must not enter, since most confined space fatalities involve would-be rescuers.

Breathing equipment that supplies air from a carried cylinder through a face mask, independent of the surrounding atmosphere. It is required where the atmosphere is unknown, inerted, or not proven safe.

Removing residues, sludge, and scale from a tank using water, chemicals, or manual methods so the tank can be gas freed, inspected, or loaded with a different product. It follows an approved procedure.

A fixed or portable nozzle assembly that sprays water or cleaning fluid around the tank interior. It allows cleaning with the tank closed, reducing the need for people to enter.

Taking out the settled residue at the bottom of a tank, often by hand with scoops and buckets. It is a high-risk task done only after gas freeing, with ventilation and continuous atmospheric monitoring.

A separate written authorization for welding, cutting, grinding, or other ignition sources. It requires gas-free certification, fire watch, and often removal of the equipment from the space.

A body harness worn by an entrant and connected to a line held by the standby person, allowing quick recovery through a small opening. It is required where rescue by other means is impractical.

A portable lifting frame placed over a tank opening with a winch for raising or lowering a person or equipment. It supports rescue and reduces strain when entering vertical tanks.

A record of who enters and leaves a space, with times, names, and purpose. It lets the standby person account for everyone inside at any moment and supports rescue and investigation.

A structured review of the hazards of a task, who might be harmed, and the controls needed before work starts. It is documented and reviewed when conditions or the scope of work change.

A short briefing before work in which the supervisor explains the task, hazards, controls, and emergency arrangements to the crew. It gives workers a chance to raise concerns.

A formal process that controls high-risk tasks by requiring written authorization, defined precautions, and sign-off before and after the job. Entry and hot work permits operate within this system.

Air containing a harmful concentration of a substance such as hydrogen sulfide, benzene vapor, or carbon monoxide. It may have no smell at dangerous levels and is detected only by testing.

A highly toxic gas found in some crude oils and sludges that deadens the sense of smell at higher concentrations. It is heavier than air and can collect in tank bottoms.

The risk of being buried or suffocated by flowing material such as sludge, grain, or powder that shifts suddenly. It is controlled by removing material before entry and by using harnesses and lifelines.