API RP 2003
Protection Against Ignitions Arising out of Static, Lightning, and Stray Currents
|Publication Date:||1 January 2008|
This recommended practice presents the current state of knowledge and technology in the fields of static electricity, lightning, and stray currents applicable to the prevention of hydrocarbon ignition in the petroleum industry and is based on both scientific research and practical experience. Furthermore, the principles discussed in this recommended practice are applicable to other operations where ignitable liquids and gases are handled. Their use should lead to improved safety practices and evaluations of existing installations and procedures. When the narrow limits of static electricity ignition are properly understood, fire investigators should be encouraged to search more diligently for the true ignition sources in instances where static ignition is unlikely or impossible.
This recommended practice is not required under the following conditions:
a) Static discharges may occur, but flammable vapors are always excluded by gas freeing or inerting the atmosphere in the area of discharge.
b) Product handling occurs in a closed system, and oxygen in that system is always below the minimum concentration required to support combustion, such as in the handling of liquefied petroleum gas (LPG).
c) The flammable concentration is always above the upper flammable limit (UFL).
This document does not address electrostatic hazards relating to solids handling. (See , , and  in the bibliography.) Vehicle fueling (truck or passenger car) is also outside the scope of this document.
Concept of Hazard vs. Risk
Hazards are situations or properties of materials with the inherent ability to cause harm. Flammability, toxicity, corrosivity, stored electrical, chemical or mechanical energy all are hazards associated with various industrial materials or situations. Charge separation and the accumulation of a static charge are inherent properties of low conductivity hydrocarbon fluids.
Risk requires exposure. A hot surface or material can cause thermal skin burns or a corrosive acid can cause chemical skin burns, but these can occur only if there is contact exposure to skin. An accumulated static charge can be a source of ignition only if exposed to a flammable fuel-air mixture under conditions where a discharge is possible. There is no risk when there is no potential for exposure to all the required elements of charge accumulation, flammable mixture and spark discharge.
Determining the level of risk involves estimating the probability and severity of exposure events that could lead to harm, and the resulting consequences. While the preceding examples relate hazards to the risk to people, the same principles are valid for evaluating risks to people, property or the environment. For instance, hydrocarbon vapors in a flammable mixture with air can ignite if exposed to a source of ignition (such as a static discharge) resulting in a fire which could injure people or damage property.
Units of Measurement
Values for measurements used in this document are generally provided in both U.S. customary and SI (metric) units. To avoid implying a level of precision greater than intended, the second cited value may be rounded to a more appropriate number. Where specific code or test criteria are involved, an exact mathematical conversion is used. Some conversions are included in Annex D.