Verify accuracy on a regular basis is to guard against any unexpected loss of sensitivity
Document!
Mandatory to use a "calibrated" instrument maintained according to "manufacturer requirements"
1910.146(c)(5)(ii)(C):
Before an employee enters the space, the internal atmosphere shall be tested, with a calibrated directreading instrument
What does OSHA accept as a "calibrated" direct reading instrument?
A testing instrument maintained and calibrated in accordance with the manufacturer's recommendations
The best way for an employer to verify calibration is through documentation
Why do instruments need to be tested and / or calibrated?
The response of gas detecting sensors can change over the life of the sensor
The changes may be sudden, or can be gradual
Substances or conditions present in the atmosphere can have an adverse effect on the sensor
Different types of sensors have different constraints and conditions which can lead to loss of sensitivity or failure
Important to know how sensors detect gas to understand conditions that can lead to inaccurate readings
Make sure the instrument has been calibrated!
Follow manufacturer recommendations
"Zero" instrument in fresh air prior to use
Verify Accuracy Daily!
Functional "bump" test sufficient
Adjust "span" only if necessary
Loss of sensitivity can be due to:
Aging or desiccation of the sensors,
Mechanical damage due to dropping or immersion
Exposure to sensor poisons present in the atmosphere being monitored
Loss of sensitivity due to other causest
Regulatory Requirements
OSHA 1910.146 requires use of a "calibrated" instrument
This means (per OSHA CPL 2.100) that the instrument must be maintained and calibrated according to manufacturer guidelines
Manufacturer Guidelines
OSHA holds instrument users accountable to maintain, calibrate and operate their instruments according to manufacturer guidelines
UL / CSA Product Markings
Typical North American Marking:
c-CSA-us or c-UL-us Classified as to intrinsic safety for use in Class I, Division1 Groups A, B, C, and D, and Class II Groups E, F and G Hazardous Locations
Class I: A location where there is a danger of explosion due to the presence of a flammable gas or vapor
Class II: A location where there is a danger of explosion due to the presence of a flammable dust
Regulatory Requirements
The safest course of action is to expose the sensors to known concentration test gas before each day
