Clearing drilled holes near loaded blasting holes

March 5, 2010

Letter #20080729-8550

Re: Does 29 CFR §1926.905(h) allow a drill to be used within 50 feet of a hole loaded with explosives when it is necessary to use the drill to open up a previously-drilled hole so that it can also be loaded?

Question: In our blasting operations, we drill a matrix of holes in the ground which are then loaded with explosives and detonated in a planned sequence. The holes may be as close as three feet to each other. We will typically drill the holes one day, then load the explosives and conduct the blasting the next day. When we proceed to load the holes, we often find that some have become filled with mud and water and need to be reopened with a drill before they can be loaded. May a drill to be used for this purpose within 50 feet of a loaded hole? 29 CFR §1926.9050; 29 CFR §1926.905(i); 29 CFR §1926.905(k).

Answer: Yes. Although §§1926.905(h) and (k) prohibit drilling within 50 feet of loaded holes, 29 CFR §1926.905(i) recognizes that activities required for loading holes are permitted in a blast area. Such activities include use of a drill when necessary to clear out a previously drilled hole to enable the hole to be loaded.

Sections 1926.905(h) and (i) provide:

(h) Machines and tools not used for loading explosives into bore holes shall be removed from the immediate location of holes before explosives are delivered. Equipment shall not be operated within 50 feet of loaded holes.

(i) No activity of any nature other than that which is required for loading holes with explosives shall be permitted in a blast area.

A related provision, 29 CFR §1926.905(k), provides:

(k) Holes shall be checked prior to loading to determine depth and condition. Where a hole has been loaded with explosives but the explosives have failed to detonate, there shall be no drilling within 50 feet of the hole.

Sections §§1926.905(h) and (k) recognize that drilling or otherwise operating equipment too close to a hole containing live explosives can cause the explosives to detonate prematurely due to vibrations produced by the drilling operation that can be transmitted through the rock. However, 1926.905(i) recognizes that the blasting operation requires that certain activities necessary to the loading of holes must be permitted in the blast area in order for the operation to proceed. Under §1926.905(i), those activities are limited to those "required for loading holes with explosives."

The scenario you describe requires that explosives be loaded in a series of holes that may be closer than 50 feet to each other. It is impermissible to load each hole immediately after it is drilled because that would require drilling within 50 feet of a loaded hole. Therefore, whenever holes are closer than 50 feet to each other, you must drill all of the holes first and then load them. When, in doing so, it is impossible to load one or more holes because those holes have become filled with mud and/or water, §1926.905(i) permits a drill to be used to clear out the hole. Use of a drill to clear out a previously-drilled hole does not present the same risk of premature detonation as would drilling away the rock itself. OSHA has previously recognized that drills are one of the types of equipment that can be used in the loading of holes within the meaning of §1926.905(h).[1]

Richard Fairfax, Acting Director

Directorate of Construction

[1]Letter of April 1, 1982 to Commissioner Robert Beard of the Virginia Department of Labor and Industry.