1-866-4 JJSTECH(1-866-455-7832)

TLV Exposure Limits

Complying with the TLV® Exposure Limit for C1 – C4 Hydrocarbon Gases

detecting instruments

C1 – C4 Aliphatic Hydrocarbon Gases

Aliphatic Hydrocarbon Gases
  • TLV® officially adopted in 2004
  • Specifies toxic exposure limit (8 hour TWA) for methane, ethane, propane and butane of 1,000 ppm
  • Has the force of law in many jurisdictions in the United States and Canada

C1 – C4 Strategy at USA Oil Industry Facilities

  • Fortunately, compliance with the C1 – C4 exposure limit is relatively easy for most oil industry instrument users
  • Most refinery instruments are already calibrated to a pentane level of sensitivity
  • Most refinery instruments have the combustible (percent LEL) alarm set at 5% LEL
  • All they need to do is change the alarm setting from 5% to 4% LEL
  • The following slides provide an explanation of why this alarm setting strategy ensures compliance with the new TLV®

How to comply C1 – C4 exposure limit

  • Fortunately, compliance with the C1 – C4 exposure limit is relatively easy for most instrument users
  • Make sure the LEL sensor is calibrated to a pentane level of sensitivity
  • Change the alarm setting from 10% to 4% LEL

Flammability Ranges and Toxic Exposure Limits for C1 – C5 Alkanes

Gas Response of sensor (calibrated to CH4) when exposed to 1% LEL of listed gasResponse of sensor (calibrated to C5H12) when exposed to 1% LEL of listed gasLEL (%VOL)
TLV (8 hr. TWA)
in ppm in % LEL
LEL reading of pentane calibrated instrument when exposed to TLV concentration of gasTrue ppm concentration of listed gas when alarm activated at 4% LEL (pentane scale)
Methane 1.02.05
1000 2.0%
4.0%1000 ppm methane
Ethane 0.751.53
1000 3.34%
5.0%850 ppm methane
Propane 0.651.32.1
1000 4.76%
6.2%670 ppm methane
Butane 0.61.21.8
1000 5.56%
6.7%595 ppm methane
Pentane 0.51.01.5
600 4.0%
4.0%600 ppm methane

C1 – C4 Monitoring Strategy

  • Choosing a pentane level of sensitivity and 4% LEL alarm setting ensures C1 – C4 TLV concentration is never exceeded
  • For methane the alarm is activated at exactly at the 1,000 PPM limit
  • For ethane, propane and butane the alarm is activated before the concentration reaches the 1,000 ppm limit
  • The 4% alarm activated by:
    • Approximately 1,000 ppm methane
    • Approximately 816 ppm ethane
    • Approximately 667 ppm propane
    • Approximately 635 ppm butane
  • An added bonus: At 4% the alarm is also activated at the TLV for pentane (600 ppm)