Authorized Gas Tester (AGT) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

LEL and UEL

The lower and upper explosive limits are the gas concentrations in air, in % v/v, between which the mixture can ignite; outside that range it is too lean or too rich to burn.

Flash point

The lowest temperature at which a liquid releases enough vapour to form an ignitable mixture near its surface; liquids below 23 °C are conventionally highly flammable.

Auto-ignition temperature

The temperature at which a flammable vapour-air mixture ignites without an external ignition source, so hot surfaces above this value can start a fire.

Vapour density relative to air

The ratio of a gas or vapour's molar mass to air (about 29); values above 1 mean it tends to settle in low points, values below 1 mean it rises.

Olfactory fatigue

Loss of the sense of smell after exposure to a gas such as hydrogen sulfide; odour is therefore never a valid method of detecting or judging gas concentration.

Vapour pressure

The pressure exerted by a vapour above its liquid; it rises with temperature, so warming a liquid can move its vapour concentration into the flammable range.

Permit to work

A formal written authorization for a defined task, location and time; it becomes invalid when conditions change, the validity period expires, or the task or personnel differ.

Authorized gas tester

The competent person who tests the atmosphere, interprets the readings against acceptance criteria, and records the results; they are accountable for the validity of those readings.

Stand-by person duties

The attendant remains outside the space, maintains communication, accounts for entrants, and initiates rescue; they do not enter unless trained, equipped and authorized.

Entry supervisor authority

The person who authorizes entry, issues and cancels the permit, confirms controls are in place, and has authority to stop work when conditions change.

Isolation before entry

Blanking, spading, disconnecting or locking off all lines and energy sources; a closed valve alone is not isolation and does not protect entrants.

Hierarchy of control

Controls ranked from eliminate and substitute, through engineering (isolation, ventilation), to administrative (permit, procedure), with PPE as the last line of defence.

Ventilation as a control

Forced air dilution lowers gas concentration but does not remove the source; continuous monitoring is still required because emission can continue during occupancy.

Permit cancellation

A positive act confirming all personnel have exited, the space is secured, and the permit is closed and retained for records; it is not simply letting the permit expire.

Catalytic bead sensor

A flammable gas sensor that measures heat of combustion on a heated bead; it reads in % LEL, needs oxygen, and is poisoned by silicones, lead and sulfides.

Infrared sensor

A gas sensor measuring light absorption at a characteristic wavelength; it is specific to a gas group, needs no oxygen, and resists poisoning but can be blinded by dirt or condensation.

Electrochemical sensor

A toxic gas or oxygen sensor generating a current proportional to concentration; it has a limited life, is temperature-sensitive, and can show cross-sensitivity to other gases.

Photoionization detector

A total VOC instrument using a UV lamp; the reading depends on the compound's ionization energy and the lamp energy, so a response factor is needed to interpret it.

Response factor

A correction applied when an instrument calibrated on one gas (usually methane) is used to measure another gas, because sensor sensitivity differs between gases.

Bump test

A brief exposure to gas above the alarm set point confirming the sensor responds and the alarm operates; it does not adjust the reading and is not a calibration.

Calibration

Adjusting the instrument reading to match a certified gas standard of known concentration, with the result recorded; it establishes accuracy, unlike a bump test.

Zero setting

Setting the instrument baseline in clean air or with zero gas; setting zero in a contaminated atmosphere biases every subsequent reading taken with that instrument.

Calibration gas validity

Certified gas must be within its expiry date, matched to the sensor's target gas, and supplied through leak-free tubing; a depleted cylinder can give a false pass.

Multi-level sampling

Testing at top, middle and bottom of the space because gases stratify by relative density; a single point sample can miss a pocket of heavier or lighter gas.

Test order: oxygen first

Oxygen is tested before flammables because a catalytic LEL sensor's reading depends on oxygen; an oxygen-deficient sample can give a falsely low reading.

Typical entry acceptance criteria

Commonly oxygen 19.5-23.5%, flammable gas below 10% LEL, and toxics below the occupational exposure limit, as set by the site procedure and applicable standard.

Continuous monitoring

Monitoring during occupancy with alarms set at acceptance thresholds; a pre-entry test is valid only for the conditions at the time it was taken.

Hot work permit

A separate authorization for welding, cutting, grinding or any spark or flame source; where a confined space is also involved, both permits must be valid and cross-referenced.

Hot work alarm threshold

A commonly used stop-work threshold is 10% LEL; if the reading reaches it, stop work, withdraw, ventilate and re-test before resuming.

Oxygen deficiency threshold

Generally below 19.5% oxygen by volume; judgment and coordination fail before the victim is aware, and below 10% consciousness is lost rapidly.

Oxygen enrichment threshold

Generally above 23.5% oxygen by volume; materials burn vigorously and a spark can cause a serious fire, so the source must be found and isolated.

Rescue plan requirement

A space-specific, rehearsed plan with equipment at the entry point and a trained team available before entry; a generic untested plan is not adequate.

Attendant rescue restriction

The attendant must not enter to rescue an unconscious entrant without breathing apparatus and training; most confined space fatalities involve would-be rescuers.