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TLV Exposure Limits
Complying with the TLV® Exposure Limit for C1 – C4 Hydrocarbon Gases
C1 – C4 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 gas | Response of sensor (calibrated to C5H12) when exposed to 1% LEL of listed gas | LEL (%VOL) |
| LEL reading of pentane calibrated instrument when exposed to TLV concentration of gas | True ppm concentration of listed gas when alarm activated at 4% LEL (pentane scale) | ||||
| Methane | 1.0 | 2.0 | 5 |
| 4.0% | 1000 ppm methane | ||||
| Ethane | 0.75 | 1.5 | 3 |
| 5.0% | 850 ppm methane | ||||
| Propane | 0.65 | 1.3 | 2.1 |
| 6.2% | 670 ppm methane | ||||
| Butane | 0.6 | 1.2 | 1.8 |
| 6.7% | 595 ppm methane | ||||
| Pentane | 0.5 | 1.0 | 1.5 |
| 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)