Explosives provide a safe and reliable way to mitigate danger trees in both fire and nonfire environments. Blasting typically is used to remove trees that cannot safely be removed using chain saws or mechanical equipment. Felling danger trees with explosives has a number of advantages, which include:

• Time employees must spend in the danger zone near the tree is limited.
  
  
• Trees can sometimes be felled in a particular direction. This is important when it is unsafe or impractical to use a chain saw or mechanical equipment.
  
  
• Multiple trees can be felled at once (figure 4). This can be critical when a hazard includes several trees requiring a timed sequence of felling events.
  
  
• Hung-up trees (trees that are supported by other trees or objects) or trees under extreme tension can be felled safely.
  
  
• Explosives can be used in wilderness areas where chain saws and other mechanical equipment are prohibited.
  
  
• Blasting leaves stumps with a more natural appearance (fuzzy stumping) than when trees are felled by other methods (figure 5).

Figure 4—A stand of trees being felled with explosives.

Figure 5—Felling trees with explosives results in a natural look called "fuzzy stumping."

Techniques

Explosives may be loaded externally, internally, or both externally and internally in some situations (figure 6).

External loading is far more common and typically is safer if the tree doesn't have existing holes or cavities for internal loading.

Figure 6—Two certified Forest Service blasters load a danger tree both internally
(using woodpecker holes) and externally with fireline explosives and emulsion.

Internal loading requires fewer explosives than external loading. Loading explosives internally typically decreases the force of the air blast. Internal loading should be used on trees that have pre-existing holes or when trees are safe to drill. Drilling holes may decrease the structural integrity of the tree, reducing safety.

Internal loading should not be used in situations where the direction of fall is important. Loading explosives internally eliminates a blaster's ability to control the direction of fall.

Qualifications

As of 2010, the Forest Service blasting program had about 250 certified blasters with another 50 blasters-in-training. The blasting program has strict requirements for certification. Potential blasters must attend a weeklong course of classroom and field exercises that is followed by an exam. Students are considered blaster trainees after completing the course and passing the written exam. Blaster trainees cannot lead a blasting operation until they have been certified by their regional blaster examiner. Trainees take 1 to 3 years to become certified blasters, depending on performance and experience.

To retain certification, blasters must:

• Attend a certification class once every 3 years
• Participate in random drug testing
• Pass a background check
• Practice blasting at least three times per year

Certified blasters must have a "Hazard Trees" endorsement on their certification cards to fell danger trees with explosives. A commercial driver's license and a vehicle with proper placards (figure 7) are required when transporting blasting materials. Blaster examiners in each region are responsible for training, coordination, and management of regional blasting programs.

Figure 7—Vehicles used for transporting explosives must display the proper placards.

Safety Issues

During fires, blasters working with felling teams can promptly mitigate trees that might be too dangerous to address by other methods. In nonfire situations, a person qualified to identify danger trees can use a global positioning system (GPS), flagging, or both to mark a number of danger trees, allowing a certified blaster to mitigate several hazardous situations quickly.

Time spent in the danger zone around a tree is limited, but the blaster must stand at the base of a tree to load explosives. Misfires are uncommon, but do occur. When a misfire occurs, protocol requires that only the blaster-incharge may approach the explosives. In most situations, the blaster-in-charge must wait 30 minutes before approaching to assess and remedy the situation. If the explosives are smoking after the misfire, the blaster should not approach the explosives for 12 hours.

Debris from a danger tree explosion usually doesn't travel as far as rock that is blasted, but the air blast still can damage structures and vehicles.

A blaster must take special precautions when working near structures or private lands, evaluating each job individually. Blasting near a riparian area may require additional analysis. Contact your regional fisheries biologist before using explosives in or around a riparian area.

Logistics

Each region has a blaster examiner and at least two qualified blasters. Certified blasters can acquire explosives in most areas of the country. Explosives usually can be ordered and delivered onsite within 1 day on most national forests. Because regional examiners and forest lead blasters maintain a relationship with local suppliers, purchasing additional product rarely is a problem. Proximity to an explosives supplier can influence a project's cost. A portable explosives magazine can be rented if a forest doesn't have its own magazine and the project requires the blaster to work in an area for an extended time period.

The area must be secured before a blast occurs. Securing an area typically entails the use of signs and the presence of guards who restrict access to the blast zone. Guards aren't required to be certified blasters. The blaster-in-charge must ensure that the guards understand their duties and all communication requirements before blasting operations begin.

The cost per tree decreases significantly when a blaster mitigates several danger trees in an area. Prior to a blaster's arrival, locate and mark all trees that are scheduled for mitigation.

A blaster may request a fire suppression crew to be present at the blast site because certain types of explosives can start fires. In order to determine which blasting materials are right for a job, the blaster will communicate with local staff to discuss the job details, site conditions, and desired results.

Contact your forest's lead blaster or your region's blaster examiner if you have questions about blasting or if blasting is required in your area (table 1).

Expected Production Rates and Estimated Costs

Production rates when blasting single danger trees can vary from one to three trees per hour (see table 3), depending on terrain and tree complexity. The amount of explosives required for each tree depends on the tree size, species, and tree complexity.

One case of fireline explosives (FLE) typically costs between $253 and $313. A case of FLE usually provides enough explosives to fell between 1 and 20 trees. Blasting caps with 8-foot leads typically cost between $6 and $7 each. A 1,000-foot spool of 50-grain detonation cord costs about $265. The number of blasts per spool of detonation cord varies, depending on the distance the blaster needs to be from each explosion.

Portable magazines rent for $50 to $450 per month. Rental companies may charge $1.75 to $2.50 per mile to transport the magazine. Companies that transport magazines for a flat rate may charge from $1,000 to $2,000 for the transportation and rental of a magazine.

Blaster pay levels may range from General Schedule (GS) 4 to 12 because employees are paid based on their primary duties. Blasting is considered a collateral duty.

Excluding travel costs, mitigation of a single tree can range from $100 to $2,000. Variables will include pay level, number of guards required, amount (and types) of explosives needed to complete the job safely, specific tree location, and general terrain.