Frequently Asked Questions
What is WR?
WR stand for the words Water Resistance and is a granular anfo explosive with a specialty surface coating. This coating
increases the water resistance and allows it to be used in wet conditions.
How does WR work?
The WR additive on the surface of the prills thickens quickly when in contact with water and forms a bridge between prills. This
forms an effective barrier which minimizes further water penetration. In addition, the “barrier” material detonates full in the
This barrier material is very close in nature to a slurry composition. When water comes in contact with WR, both air and fuel
are captured and held in place, as a result of the quick swelling action. This material can be considered ”insensitive” slurry,
which detonates fully with the aid of the dry prills in close proximity. Water in the barrier material is converted to steam in the
detonation process and results in higher borehole pressures. Higher borehole pressures translates into more heave and
better fragmentation. In fact, WR in wet conditions produces better results than in dry conditions, because of its effective
usage of absorbed ground water.
Is dewatering required with WR?
Generally, dewatering before loading WR is required. If there is standing water in the boreholes, then it is necessary to
dewater. This is because the same process that keeps water from penetrating into WR, can also keep WR from pouring
through water. This will lead to bridging and water-filled gaps in the borehole, which can lead to cutoffs. In addition, WR gets
much of its strength by shooting dry in wet conditions. By pouring through water, all prills become wet and negate this
advantage. However, if the boreholes are just wet and dripping and there is still no substantial standing water before loading,
dewatering may not be required.
How does WR save me money?
The usage of WR can reduce your overall blasting costs and production costs. First, WR can reduce the usage of more
expensive emulsions by 40-80% and replace it with more economical WR. Secondly, because WR has “full borehole
loading”, you get more pounds per foot of explosive per borehole, which will give you better heave and fragmentation. And
third, WR is all energy and has no inert water in its composition, which means more energy per dollar of explosives. These
all add up to saving on both explosives and production costs!
What about VOD and density?
The velocity of detonation of WR tends to be about 5-7% faster than the anfo it is made from based in the corresponding
borehole diameter. Geological conditions may also play a role in VOD as it does for all explosives. VOD testing of WR at the
Demenigoni Project in Hemet, CA showed velocities to average about 14,700 ft/s in 6 ¾ inch boreholes.
The density of WR Anfo depends on the density of the anfo used for its manufacture. Typical anfo has a density around .82 g/cc.
The density of WR is only slightly higher, about .84 g/cc, as a result of the additive. However, low-density ammonium nitrate
prills with both lighter and heavier densities in this category can be used to produce WR. In some cases it is possible to use
high-density ammonium nitrate with WR, but prill size is important. It is recommended to contact Adtec directly if other than
low-density prill use is anticipated.
Can WR be used with bulk mixing and loading?
Yes. WR was used very successfully with bulk loading at the recent Demenigoni Project in Hemet, CA. The basic loading and
dewatering procedures still apply and will give equally good results.
How long can WR sleep?
Since the water resistance of WR is accomplished by the quick swelling of the surface coating and barrier formation, it is helpful
to understand the nature of this barrier. Initially, when the barrier is first formed from water penetration, it is about ¼ to ½ inch in
thickness. It is soft in its texture and will hold back water from penetrating into the explosive column. However, the barrier
continues to grow very slowly in thickness with time, in a process similar to osmosis. The initial rate of growth is about ½ inch
per 24 hours, becoming slightly less in following days. Therefore, WR is designed to be loaded and shot on the same day.
However, many shots have slept overnight, and even over the weekend, with excellent results. But the time factor should be kept
What kind of dewatering equipment will I need?
Dewatering pumps most commonly used with WR are BDS, Dryrite and Legra. BDS is an economical pump, which utilizes
pressurized air from a drill compressor and an inflatable bladder to seal a borehole and force water out. This method works well
and is the most economical pump. However, in fractured geology compressed air is able to escape around the seal and the
effectiveness of this pump is reduced or made inoperable. The Dryrite pump is a double diaphragm pump, which dewaters
boreholes through suction and a special dewatering nozzle. This pump works in all types of geology, including fractured rock.
Legra is a hydraulic pump for 6” and larger boreholes. It is normally mounted on a pickup truck or bobcat. Its advantages
include faster dewatering, especially at lower depths. Disadvantages include higher initial cost, higher wear and maintenance
factors and high cost of losing a hydraulic pump head down the borehole.
In addition to the above mentioned dewatering pumps, it is possible to simply shove an airline down the borehole, turn on the
compressor air and allow the water to “rain down” around the hole. Unfortunately, this is quite messy and the reason most
blasters invest in dewatering equipment. Although dewatering requires some extra time, often the time spent on dewatering can
be made up through faster borehole loading times, and avoiding problems of loading through water. Borehole collars are
recommended during dewatering as it will reduce the potential of rock falling into the borehole during dewatering and losing a
What kind of projects and geological conditions is WR suitable for?
Construction. WR has found many popular application in the construction industry. Trenching is one of the most common
applications. Often shallow wet and dripping trenching boreholes cause anfo misfires. WR gives great protection in these
situations and often may not require dewatering. WR also gives protection against rain runoff and other weather-related loading
problems encountered in construction projects. Road construction is another popular use of WR. In the Northwest US and
Western Canada WR is the preferred explosive for construction of logging roads. With the high natural rainfall in this geographic
area, most every shot must contend with water conditions. WR has become the leader in this highly competitive and
Quarries. WR is commonly used in many quarry situations. The usage of WR may be used to help reduce the usage of more
expensive slurries and emulsions stick products. In addition, the full borehole loading of WR produces excellent fragmentation
Permafrost. WR has good application in cold northern climates with permafrost. Anfo in permafrost conditions tends to melt
the frozen ground, which leads to the formation of a dense ammonium nitrate solution in the bottom of the boreholes. This can
lead to misfires and cutoff. WR is used to eliminate these problems by reducing melting. In addition, WR does not have to be
maintained at warm temperatures for usage during exceptional cold weather.
Difficult Geology. Certain difficult geological situations may also be good applications for WR. In the recent construction of the
Domenigoni Resevoir Project in Southern California, difficult geological conditions were encountered. Alternating layers of hard
and soft metamorphic rock formations (quartzite and gneiss) were combined with fracturing and water conditions. Soft rock
formations tended to absorb shock energy of emulsions, while the more water-resistant emulsions do not produce enough
gas heave, for adequate displacement and excavation. Onsite testing showed that WR Anfo produced better results that 30/70
emulsion with the same drilling pattern and borehole size in these conditions. WR was chosen as the primary explosive
because it produced the best combination of water resistance, shock energy and heave.