Fumes
The fume class of an explosive is the measure of the amount of toxic gases produced in the detonation process. Carbon monoxide (CO) and oxides of nitrogen are the primary gases that are considered in the fume class ratings. Carbon monoxide is a colorless and odorless gas that in sufficient concentrations can displace oxygen in the blood, depriving organs and brain of required oxygen. Although most commercial blasting agents are near oxygen balanced to minimize fumes and optimize energy release, fumes will occur, and the blaster should be aware of their production. In underground mining or construction applications, the problems that can result from producing fumes with inadequate ventilation is obvious and can be deadly. It should be pointed out that in surface operations, especially in deep cuts or trenches, fume production and retention can also be hazardous to the personnel on the job as ventilation may not be sufficient to displace CO generated by the blasting. Certain blasting conditions may also produce toxic fumes even when the explosive is oxygen balanced. Some conditions that can cause toxic fume production are insufficient charge diameter, inadequate water resistance, inadequate priming, and premature loss of confinement.
The Institute of Makers of Explosives (IME) have adopted a method of rating fumes. The test is conducted by the Bichel Gauge method. The volume of poisonous gases released per pounds of explosives is measured. If less than 276 in3 of toxic fumes are produced per 0.44 pounds of explosives, the fume class rating would be 1. If 276 in3 to 570 in3 of poisonous gases are produced, the fume class rating is 2, and if 570 in3 to 1,158 in3 of poisonous gases are produced, the fume class rating is 3. Table 5 lists fume ratings of commonly used explosives.
Strictly speaking, carbon dioxide is not a fume since it is not a toxic gas by itself. However, many deaths have occurred over the years due to the generation of large amounts of carbon dioxide during blasting in confined areas. Although carbon dioxide is not poisonous, it is produced in large quantities in most blasts. In sufficient concentrations it has the effect of causing the involuntary muscles of the body to stop working. In other words, the heart and lungs would stop working if one was placed in high concentrations of carbon dioxide. If concentrations are 18% or higher in volume, death can occur by suffocation. An additional problem with carbon dioxide is that it has a density of 1.53 as compared to air and it would tend to pocket in low places in the excavation or where there is little movement of air. A simple solution to the problem is to use compressed air or ventilation fans to dilute any possible high concentrations in depressions of trenches.
A special note should be made here regarding ANFO and the fuel oil content on production of fumes at the site. Due to production methodology there can be some variability in the oil content in the ANFO prills. Particular attention should be paid to “red/orange fumes” where there is no water as this may indicate production of nitrous oxides. If carbon black appears on rocks after a blast or there are very dark grey gases, production of carbon monoxide may be suspected. CO content of the air can also be tested. Rowland and Mainiero in 2000 (Rowland and Mainiero, 2000) performed testing on types of fume productions depending on the oil content. Generally, where ANFO prills are too dry there will be increasing Nitrous Oxide fumes, where the prills are too wet, there is increasing Carbon Monoxide fumes. This can be an important safety consideration on a project. Testing can be performed to check the ANFO prill oil content. If other factors are well controlled, and there are still indications of a problem such as blasting gas color, or tests indicate excessive CO, ANFO product should be tested.
