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Gases Characteristics
Sensor Characteristics
   
 

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Table of Contents

C CE - Ceiling Limit
I IDLH - Immediately Dangerous to Life or Health
L LEL - (Lower Explosive Limit) Example (Methane gas)
  Linearity
N NEMA Type
  NEMA Type 4
  NEMA Type 4X
  NEMAType 12
P PEL - Permissible Exposure Limit - OSHA
R REL - Recommended Exposure Limit - NIOSH
  Repeatability
  Response Time
S Safety Group (refrigerants)
  STEL- Short Term Exposure Limit
T TLV - Threshold Limit Values - ACGIH
  TWA - Time Weighted Average

CE - Ceiling Limit

The concentration which should not be exceeded at any time.

IDLH - Immediately Dangerous to Life or Health

The IDLH value is based on the ability of a worker to escape without loss of life, irreversible health effects, or other health effects such as disorientation or coordination that could prevent escape.  It is the maximum concentration allowed before which a highly reliable breathing apparatus providing maximum protection for workers in required.

LEL - (Lower Explosive Limit) Example (Methane gas)

Methane gas has a LEL of 5.53% by volume. If the atmosphere has less that 5.53% methane, an explosion cannot occur even if a source of ignition is present. When the methane concentration reaches 5% an explosion can occur if there is an ignition source. Each combustible gas has it's own LEL concentration.

Linearity

Quantitatively, refers to the output signal in relation to the gas concentration.

NEMA Type 1

For general-purpose indoor use. Provides protection against incidental contact with the enclosed equipment.

NEMA Type 4

For indoor or outdoor use. Provides protection against windblown dust, rain, sleet and ice. Provides rust resistance. Provides protection against direct water hosedown.

NEMA Type 4X

For indoor or outdoor use. Provides protection against windblown dust, rain, sleet and ice. Provides rust resistance. Provides protection against direct water hosedown. Provides corrosion resistance for indoor use.

NEMA Type 12

For indoor use. Provides protection against dust, falling dirt and dripping non-corrosive liquids.

PEL - Permissible Exposure Limit - OSHA

TWA permissible concentrations, to which workers may be exposed continuously, day after day, without adverse effects, for a normal eight-hour workday and a forty-hour work week.

REL - Recommended Exposure Limit - NIOSH

The TWA concentration permissible for up to ten-hour workdays during a 40 hour work week.

Repeatability

Relates to the ability of sensors to repeat the measurements of gas concentrations when the sensors are subjected to precisely calibrated gas samples.

Response Time

The time required for a sensor to read a certain percentage of full-scale reading after being exposed to a full-scale concentration of a given gas. Example: T80 = 30 seconds means that a sensor takes 30 seconds to reach 80% of the full scale reading after being exposed to a full-scale gas concentration.

Safety Group (refrigerants)

This is determined by a combination of flammability and toxicity. "A1" rating denotes the safest refrigerants to handle and "B3" denotes the most dangerous. Combustible alarm systems are set to alarm at a low percentage of the LEL of the target gas.

STEL- Short Term Exposure Limit

A fifteen-minute TWA exposure which should not be exceeded at any time during a work day even if the eight-hour TWA is within limits. Exposures at the STEL should not be longer than fifteen minutes and should not be repeated more than four times per day. There should be at least 60 minutes between successive exposures at the STEL.

TLV - Threshold Limit Values - ACGIH

TWA permissible concentrations, to which workers may be exposed continuously, day after day, without adverse effects, for a normal eight-hour workday and a forty-hour work week.

TWA - Time Weighted Average

The average concentration of contaminants over a specified time period.

 
Published: February 16, 2004 Last Updated: April 26, 2004