Understanding Static Electricity in Entry Ventilation
General industry needs a clear, well-defined "how to" standard explaining how to control and safely remove electrostatic charges during ventilation.
- By Dave Angelico
- Feb 01, 2005
WORKING in tanks, manholes, and underground vaults are some of the most dangerous and potentially lethal occupations found in the industrial work environment. Federal, state, and corporate safety departments have written reams of documents and procedures on how to enter a confined space safely and perform some sort of maintenance, repair, or cleaning operation.
Good corporate work practices and procedures have existed for years at the industry-specific level. The phone companies, chemicals, pharmaceuticals, and oil storage and refineries long have seen the necessity of a "how to" manual for work on their own specific confined space hazards. The current OSHA Standard, 1910.146, Permit-required Confined Spaces, goes a long way toward providing general industry the framework for entering and exiting a confined space and identifying some of the hazards a worker may encounter.
This OSHA standard was the outgrowth of many existing standards that came together to provide a minimum for general industry to follow. The one process needed in the standard is a specific work practice for the safe removal of static electricity during confined space ventilation and a means to test it. This work practice should be simple enough for all industry trades to be able to perform it.
Meeting Industry Demands
Manufacturers have to be responsive to the wants and needs of their customers. We have constantly been asked by companies, contractors, military officials, and consultants, "How do you properly handle the potential problem of static electricity build-up when you are ventilating a tank or manhole?" The art and science of ventilation has many books and articles to help in the quest for understanding the many ventilation techniques used in industry, however, the one area that is very sketchy involves ventilation and the potential disastrous problems of electrostatic charges.
Many of the corporate and government procedures say static charges should be removed, but few tell the worker how to do it. After reviewing a great many standards and procedures, it appears the best source for understanding this phase of the confined space ventilation procedure comes from an industry-specific source, ANSI/API Standards 2015 and 2016, published by the American Petroleum Institute in Washington, D.C. Another excellent source is NFPA 77. These documents provide requirements and actual procedures for safe entry and work in confined spaces; more specifically, they address the issues with regard to controlling static electricity. The only ingredient missing from these standards is the aspect of how to set up and test a complete grounded ventilation system.
Static Electricity: The Basics
At some time in our lives, all of us have all felt the effect of static electricity build-up. Simply walking across the living room carpet and touching a metal doorknob or refrigerator causes us to feel and see the spark of discharged static electricity.
Static is generated whenever two dissimilar materials are in relative motion to each other. I recently was filling my car's tank with gasoline and saw a warning notice on the gas pump. The manufacturer of the pump plainly and simply explained that if I get out of my car to put fuel in the tank, I should not get back in the car with fuel pumping until I touched the front frame of the car and discharged any potential build-up of static electricity--or a resulting explosion could occur.
About a year ago, a safety director at an Ohio hospital complex called me after he purchased an explosion-proof blower, an air conduit device, and conductive ducting. He asked how he should test the system to ensure he was achieving a good ground and that he was dissipating static electricity. He told me every ventilation system in the hospital had to be tested to assure a good ground. These examples brought to my attention the need to address the specific treatment of the problem of static electricity in ventilation.
Free electrons will be attracted to any other electron-deficient nucleus. Movement of electrons from one atom to another constitutes electrical energy, including static electricity. What causes these electrons and static charges to migrate from one atom to another? This movement of static charges is due to such factors as a small change in temperature, atmospheric pressure, relative humidity, and the friction of air through a piece of ducting. The energy needed to cause this movement of atoms is surprisingly very low.
Even though all matter contains free electrons, these electrons are unable to move freely through materials with high electrical resistance, which are called non-conductors or insulators. Examples of non-conductors are glass, gases, rubber, and many plastic materials.
Standard non-conductive vinyl ducting, the traditional industry standard, is used in most confined space ventilation applications. Even if it is properly grounded, the displaced electrons become trapped on the surface of the ducting. When a substance of opposite polarity comes in contact with a non-conductive device, the trapped electrons can flow freely between the two materials. This sudden and rapid transfer of electrons can cause a spark of sufficient intensity to ignite a confined space that may contain industrial solvents, methane gas from decaying material, hydrocarbon residue, or fine airborne dust.
NIOSH says a low relative humidity--below 50 percent--can accelerate the build-up of electrostatic charges, creating sufficient energy to ignite flammable atmospheres. Abrasive blasting operations in confined spaces can cause a tremendous build-up of static charges by the mechanical friction of the blasting material, which can provide the charge necessary to cause an intense explosion of the dusty space. NFPA says if a hazard exists or has a potential to exist, the work environment should be evaluated with regard to the potential of static electricity build-up.
The following questions need to be asked:
1) Can a static charge be generated?
2) Will the charge be able to accumulate?
3) Can a discharge of static electricity occur?
4) Will an ignitable mixture be present at the site of the discharge?
5) Will the discharge have sufficient energy to ignite the mixture?
The Proper Ventilation System
NFPA, OSHA, and ANSI/API standards say good work practices in a confined space necessitate continuous ventilation before and during the work performed in a confined space. The objective of a good ventilation system is to first gas free the confined space, then to stabilize the space by providing continuous fresh air to the workers.
ANSI/API recommends the use of a venturi type eductor air mover or an explosion-proof electric blower when working in an explosive or potentially explosive environment. The electric motor and on/off switches must be approved, at a minimum, for use in Class I, Division 1, Group D atmospheres for methane and Class II, Division 1, Groups E, F, and G for dust hazards. Each blower selected must have a metal grounding lug located on the blower. This lug is used to connect the ducting and its wire helix to the blower to form an electrical bond. Ducting should be supplied with fabric manufactured with a conductive coating material and a 12-inch grounding wire attached to the metal helix inside the duct and installed at each end of the duct.
The bonding process is simply where metal components in the ventilation system are connected to form a conductive path that ensures electrical continuity and the flow of static electricity back to a safe grounded source--the blower. In performing tank work, the entire blower system is bonded to the tank that is connected to a proper earth ground. ANSI/API Standards 2015 and 2016 detail how the use of a venturi style eductor along with an electric blower can be used to accomplish a preferred push/pull method of confined space ventilation. The one aspect of this ventilation set-up that is missing is how to test the entire system for a good electrical ground once it is in place. What levels of resistance (ohms) are sufficient to remove static charges?
Part of a good confined space entry program is having met key objectives listed in the OSHA 1910.146 and ANSI/API standards; one important objective is the aspect of self-rescue. The use of an air conduit device allows a worker to establish continuous ventilation in the confined space without obstructing the entry or egress of the workers. This device meets the objective of self-rescue for the workers who may encounter hazardous work environments. The second key objective is to provide a ventilation system that eliminates the build-up of static electricity and potential ignition hazard and provides for a safer work environment. With a 90-degree elbow, the device in conductive polyethylene material connects to sections of conductive ducting. When properly assembled, it forms a complete electrical circuit (bond) from the farthest end of the duct all the way back to the grounded ventilation blower. Electrostatic charges that traditionally would build up on the surface of the ventilation system are now safely removed through the ventilation system.
Prior to the start of the ventilation process, the entire blower system must be set up and tested. A lead from a volt/ohm meter should be attached to the farthest end of the ducting and its metal helix and the other lead should be attached to the metal housing of the blower. The volt/ohm meter should provide a reading between 50K and 350K ohms. This range will provide adequate resistance for the static charge build-up to drain to a properly grounded source through the blower's electric cord.
Confined space entry is hazardous for even the most seasoned professionals. Unfortunately, most of the work done in confined spaces is done on an occasional basis with less-than-expert workers. It is only a matter of time before all of the right conditions of fuel, oxygen, and ignition come together to form another frightening newspaper or magazine headline.
We believe OSHA needs to seek the guidance and expertise of industry professionals to write additional "how to" procedures to aid and assist the occasional confined space worker on handling and removing static electricity when ventilating. Using air conduit devices will eliminate one more potential hazard from the confined space worker's list of potential problems.
This article is only the beginning in an effort to bring to light the need for more help in the area of worker safety with regard to confined space entry. Industry professionals from many disciplines must work together to develop safe working procedures for general industry with regard to controlling static electricity in the work environment. A detailed, step-by-step method must be developed to set up and properly test the conductive ventilation system.
This article appeared in the February 2005 issue of Occupational Health & Safety.
This article originally appeared in the February 2005 issue of Occupational Health & Safety.