What are Hazardous Substances?

Are defined as chemicals capable of causing adverse health effects to people. Examples include benzene, asbestos, hydrochloric acid. Look for the Risk and Safety Phrases on the label, SHOC Card or MSDS. Ideally the MSDS will stipulate whether the chemical is hazardous or not.

What are Heavy Metals?

Mercury is a trace component of geologic hydrocarbons including coal, crude oil and natural gas.

Mercury in natural gas processing systems and above certain concentrations can deposit in, and thus contaminate, equipment, treatment fluids and process waste streams. Maintenance and inspection activities, therefore, must contend with mercury contamination from a health and safety standpoint and such activities also must be structured to avoid escape of mercury into the environment.

What are Occupational Exposure Limits?

Occupational Exposure Limits refer to airborne concentrations of chemical substances to which nearly all workers may be repetedly exposed, day after day, over a working lifetime, without adverse health effects.

There are three categories of exposure limits:-

• Time-Weighted Average (TWA)
• Short-Term Exposure Limit (STEL)
• Peak or Ceiling Limit

The exposure limits PDO adopts are taken from the most current edition of the ACGIH Threshold limit values for Chemical Substances. Where Shell adopts a more stringent exposure limit, these values will be included in the SHOC cards.