Elaborate on the proper calibration and usage procedures for a multi-gas meter used for atmospheric monitoring in confined spaces, including actions to take upon encountering specific alarm conditions.

The proper calibration and usage of a multi-gas meter are essential for ensuring accurate atmospheric monitoring in confined spaces. A multi-gas meter is an instrument designed to detect various gases, such as oxygen, flammable gases, and toxic substances like hydrogen sulfide and carbon monoxide. Calibration is a critical process that confirms the meter's sensors are functioning correctly and providing accurate readings. Improper calibration can lead to inaccurate readings, thus potentially exposing workers to hazardous conditions.

Calibration is usually performed in two stages: bump testing and full calibration. A bump test is a quick check to ensure that the meter's sensors respond to a known concentration of gas. It involves exposing the sensors to a gas mixture and ensuring that the readings fall within an acceptable range. This test is typically performed before each day of use, or before each entry into a confined space. A full calibration is a more detailed process which calibrates all the sensors and adjusts them for optimal performance. It involves using a calibration gas with a specific concentration and adjusting the meter's readings to match this concentration, ensuring accuracy across the detection range. This calibration is done at regular intervals specified by the manufacturer, typically every 30 to 90 days depending on the meter type and usage. Calibration often involves a controlled environment where the meter will be set to zero and exposed to a known amount of the target gas or gases to ensure the sensor reading is correct.

The usage procedure for a multi-gas meter in a confined space typically involves the following steps: Before use, the meter must be fully charged and bump-tested. The user will turn on the meter and allow it to stabilize and zero in a fresh-air atmosphere, as this sets a baseline. The meter's sensors must then be exposed to the atmosphere in the confined space, and this can be done either by lowering a sample hose into the space, or, if possible, by extending the meter into the space to take the reading. Readings must be taken from various levels of the confined space since gases may stratify (settle in layers) due to differences in density. For example, heavier-than-air gases, like hydrogen sulfide, will sink to the bottom, and lighter-than-air gases like methane will rise to the top. The user then will observe the readings and check for any warnings, such as a low battery, calibration due date, or alarm setpoints. If the meter is being used by someone unfamiliar with confined space protocols, they should consult with their supervisor or a safety officer to confirm the meter is working correctly and is used properly for the work being done.

When specific alarm conditions are encountered, actions must be taken immediately. Different alarm conditions can include low oxygen readings, readings above the LEL for flammable gases, or readings above the permissible exposure limits for toxic gases. Different meters will have varying alarm settings. If the oxygen level drops below 19.5%, this indicates a deficient atmosphere and entry is not allowed. If the meter alarms to dangerous levels of flammable gases, all sources of ignition must be removed and ventilation measures must be taken before retesting. If toxic gases are present above their permissible exposure limit, then appropriate respiratory protection is needed, and steps to remove the toxic materials or properly ventilate the area must be taken. In any alarm situation, work must stop immediately. The meter should be removed and the work area must be reevaluated to determine if it's safe to proceed. Sometimes, this means bringing in additional ventilation equipment, or having additional safety personnel present, or even ceasing operations. Alarm conditions must never be taken lightly and should trigger immediate action, often including evacuation and consultation with a qualified safety professional or site supervisor to re-evaluate the plan and make changes as needed. These steps ensure that a reading or alarm condition is not ignored and that workers are always protected.