The propellant is the primary source of the sound impulse generation from firearms. When a propellant is ignited, a three-step transformation of chemical energy occurs: (1) a chemical propellant converts to a gas, (2) a thermodynamic driven motive-power (heat to mechanical energy) is released, and (3) then physical energy in the form of hot gases pushes the projectile which releases energy that produces torque and recoil due to the reactive force and friction between the barrel and the projectile (Rinker, 2005). As the hot gases expand in the chamber, increased pressure pushes the projectile down the barrel and out of the muzzle. Multiple acoustic events may occur; the primer ignites the powder behind the projectile, the powder ignition produces the muzzle blast in the chamber and as the gases expand out of the muzzle; supersonic projectiles produce a shockwave with a characteristic N-wave heard as a sharp audible “crack.” A number of variables can impact the impulse acoustic characteristics including firearm make and model, ammunition type, barrel length, and muzzle brakes or ports. In the case of starter pistols, a blocked barrel eliminates the muzzle blast sound source from an open barrel and requires the high-pressure gases to find alternative routes of escape. Additionally, there is no projectile and therefore the supersonic source is also eliminated.

The terms hazard and risk are often used interchangeably, but they refer to different concepts. For the purpose of this paper, the term hazard is used to indicate a sound that is a potential source of auditory system damage. The term risk was used to quantify the likelihood of harm. Knowledge of the risk posed by a hazard informs the development of damage-risk criteria, (DRC) which are used to derive the limits of exposure necessary to reduce the probability of a noise-induced hearing loss of a given magnitude (e.g. a 25 dB permanent threshold shift) for a specified proportion of the population (e.g. the least susceptible 95%), with a known certainty (e.g. 95%). For brief signals such as starter pistol impulses, the DRC permit the transformation of signal parameters into a number of individual shots or maximum permissible exposures, or MPE. MPEs represent the limits beyond which a greater amount of hearing loss, in a portion of the adult population, or in instances of less than 95%, certainty would be expected.

Handgun weapons firing blanks are often presumed to be inherently harmless and eliminate the risk of injury and/or death from a bullet or other projectile. Starter pistols are largely unrestricted in terms of sale and carry for adults over the age of 18 years (Giese et al, 2002); however, local regulations may vary. In reality, blank cartridge handguns fired at a close distance are capable of inflicting serious or lethal injury (Buyuk et al, 2009; Jacob et al, 1990; Giese et al, 2002; Rothschild et al, 1998b; Rothschild & Vendura, 1999). In addition, acute acoustic trauma as a result of impulse noise exposure from weapons firing blanks has been reported (Fleischer et al, 2003; Savolainen et al, 1997). U.S. President and well-known movie actor, Ronald Reagan, provided a televised public service announcement in 1990 discussing his hearing loss as a result of acoustic trauma from firing blanks with a firearm (without wearing hearing protection) while acting in a movie production.

The auditory hazard is seldom recognized for the starter pistol operator and people nearby as compared to an open barrel “real” firearm of the same caliber and barrel length. However, there is a potential for a starter pistol to produce more sound pressure (and therefore more auditory hazard) than a real firearm with the same dimensions and combustible material. This is because none of the energy released through combustion is converted into the kinetic energy of a projectile, which accounts for approximately 3–40% of the chemical energy contained in the propellant (Warlow, 2005). In addition, sound levels may also be increased due to the use of plugged barrels, short barrels and open chambers/cylinders in starter pistols.

Impulses from firearms are often described in terms of instantaneous peak sound pressure levels (SPL). In order to prevent cochlear damage and resultant noise-induced hearing loss (NIHL) from impulse sounds, the World Health Organization (WHO) recommends an unprotected limit of 140 dB peak SPL for adults and 120 dB SPL for children (WHO, 1999). Multiple U.S. government agencies, including the National Institute for Occupational Safety and Health (NIOSH, 1998), the Occupational Safety and Health Administration (OSHA, 1983), the Mine Safety and Health Administration (MSHA, 1999), the Federal Railroad Administration (FRA, 2007), and the Department of Defense (MIL-STD-1474D,1997) reference a limit of 140 dB peak SPL for adults. The European Union Directive 2003/10/EC (2008) also limits exposure at 140 dB C-weighted. Internationally, 120–140 dB peak SPL limits (weighted or unweighted) are referenced in the international occupational noise exposure standards for Australia, Brazil, Chile, Columbia, India, Israel, Netherlands, New Zealand, United Kingdom, and Venezuela (Suter, 2007). Peak levels from firearms shooting projectiles usually exceed these limits for both the shooter and the bystander (Flamme et al, 2009b, 2011; Kardous et al, 2003; Murphy & Tubbs, 2007; Odess, 1972, Ylikoski et al, 1995, and the current authors’ unpublished data, 2012). In recent studies, mean peak levels for firearm impulses ranged from 141–167 dB SPL at the shooter’s ear and at a bystander position to the left of the shooter for a subset of civilian firearms and ammunition, (Flamme et al, 2009b, 2011). Rothschild et al (1998a) reported the peak sound pressure levels from 15 different models of starter pistols at four azimuths (0° shooting direction, 45°, 90°, and 180°) and four distances from the muzzle (25 cm, 50 cm, 100 cm, and 200 cm). All weapons exceeded 160 dB peak SPL at a distance of 1 meter and in the 0° shooting azimuth.

An alternative equivalent-energy approach may also be used to describe the sound hazard from impulse noise in terms of L_eqA8 (Atherley & Martin, 1971). This criterion is based upon filtering the acoustic signal to approximate the transfer function of the human ear at 40 phons and integrating the energy over time. Most regulatory agencies utilize this approach for establishing the 85 or 90 dBA time-weighted average (TWA) permissible noise exposure limits for both continuous and impulsive noise sources in the workplace (NIOSH, 1998; OSHA, 1983). There is no specific DRC developed for application to children.

Motivation for the current study came from an inquiry from a high-school track and field official advocating for the use of safer means of starting races than the traditional starter pistols. This official was interested in addressing concerns expressed by the physician director of the state-level athletic association, and the lack of peer-reviewed evidence indicating that starter pistols are potentially hazardous to the official and/or student athlete. A series of three experiments were conducted to further explore the acoustic properties and risk of NIHL from starter pistols. Specifically, (1) acoustic directionality was measured for two .22 caliber starter pistols; (2) acoustic comparisons of the impulses generated from typical .22 and .32 caliber starter pistols firing blanks were made to impulses generated from comparable caliber revolvers firing both blanks and standard-velocity live ammunition and (3) a simulated track and field measurement for both a .22 and .32 caliber starter pistol.

One purpose of this research effort was to evaluate the sound levels produced by starter pistols and assess potential auditory hazard to the shooter or to people near the sound source. A variety of procedures are available for examining auditory risk (i.e. the probability of harm resulting from a hazardous exposure), ranging from early methods relying on the empirical relationship between changes in human hearing and (1) the fine structure of the impulse stimulus (e.g. Coles et al, 1967), (2) the overall (i.e. integrated) impulsive sound energy (e.g. Dancer, 1982; Smoorenburg, 2003), and (3) models estimating the type and degree of mechanical motion produced by the impulse (e.g. Price, 2007). Based on recent evaluations of a variety of DRC for impulsive noise (Murphy et al, 2009, 2011) and based on the observation of strong correlations among the DRCs (Flamme et al, 2009b), the study adopted the use of integrated impulsive sound energy as our metric of auditory risk for the purposes of this paper. The maximum allowable level used for this paper is 85 dBA L_eq in accordance with a well-known standard of this type (Direction Technique de Armements Terrestres (DTAT), 1983). Interested readers may wish to consult Flamme et al (2009a) for further explanation of the various DRCs as applied to adult subjects.

This study was conducted to evaluate the assumption that starter pistols are intrinsically safe for users (sports officials), spectators, and athletes in sporting events. Starter pistols (.22 and .32 caliber) were examined with respect to the directional characteristics of the impulse noise they generate when fired (Experiment 1), their sound emissions relative to comparable firearms (Experiment 2), and the degree of exposure produced for the shooter and athletes at three shooter positions on a simulated sprint track (Experiment 3).

The two starter pistols used in the directionality experiment exhibited similar characteristics. When measurements were centered on the apparent muzzle end of the starter pistol barrel, it appeared that more sound was directed back toward the shooter. However, if peak levels were adjusted for the distance between the muzzle and the lateral end of the firing cylinder (centered on the firearm), the levels observed would likely be similar in all directions—and might suggest essentially spherical propagation at distances of 50 cm and beyond. The small difference in length between the tip of the barrel and the physical “center” of the pistol are significant when measuring levels in the near-field. Figure 6 illustrates the orientation of the starter pistol during starter official firing and the elevation of the pistol above and angled away from the athletes provides for the sound source escaping from the chamber area and radiating back towards the shooter’s ear.

Starter pistols produce more sound at the shooter’s ear than normal open-barrel guns firing either live ammunition or blanks. The magnitude of the difference varied with caliber, with a greater difference and level at the shooter’s ear for .22 caliber cartridges. However, the levels 1.5 m downrange and beside the exit chambers were nearly identical across calibers of starter pistols. While the differences between these starter pistols is likely due to the design characteristics of the individual models used in this study, these findings suggest that lower sound levels should not necessarily be expected from smaller-caliber starter pistols. This is important when considering the suggested use of .22 caliber starter pistols for indoor sporting events.

As expected, based on the comments of Warlow (2005), sound levels downrange of open-barreled guns were lower when a projectile (i.e. bullet) was fired because of the energy expended to accelerate the projectile. However, sound levels at the shooter’s ear and to the side of both the cylinder and muzzle tended to be higher when live ammunition was used. It is possible that this finding stems from the exclusive use of revolvers in this study. The projectile is accelerated due to the pressure differential across the bullet. As the rear end of the projectile passes through the gap between the cylinder and barrel in the revolver, the pressure might be more easily able to escape through the gap than to continue propelling the projectile down the barrel, and this could lead to greater sound levels to the side of the firearm. However, it is possible that this result will not be observed in firearms without a cylinder gap (e.g. single-shot or semi-automatic action firearms).

The numbers of maximum permissible exposures (without protection) near the shooter (Tables 3 and 5) confirmed that unprotected ears of a shooter firing a starter pistol are likely to be at an elevated risk of noise-induced hearing impairment. At the shooter’s ear, a maximum of five to twelve unprotected .22 caliber starter pistol exposures per day would be allowable. This number of permissible shots could be exceeded during routine track and field events at both the high school and collegiate level. Track events with a larger number of races and a greater number of heats would create a more hazardous exposure condition for the official. False starts or timing recalls would further increase the auditory risk for an unprotected official.

Peak sound pressure levels measured at athlete positions exceed the WHO criteria of 120 dB for both the .22 and .32 caliber starter pistols. When measured outdoors, the numbers of maximum permissible adult exposures in the simulated track experiment suggest that athletes are at a low risk for NIHL at the static starter locations included in this experimental design. However, spectators near the starter are at a substantially elevated risk for hearing loss if hearing protection is not used. Athlete risk may also be different depending on their position relative to the pistol when fired for last lap or recall signals. Clinical reports of hearing loss as a result of a single impulse exposure from a firearm shooting blanks have been reported in the literature; however, none of these reports involved exposure at an athletic event (Fleischer et al, 2003; Savolainen et al, 1995). It may also be worth considering that the MPE calculations are based upon research outcomes with adult subjects and were not designed with specific application to ears of younger children. There are no impulse DRC developed specifically for the young ear. Recent animal research with non-impulsive noise suggests that a young noise-exposed group may demonstrate accelerated “age-related” hearing loss in later life when compared to a non-noise exposed group (Kujawa & Liberman, 2006). The amount of “material” hearing impairment may also differ when considering adult versus child listeners. Consequently, it is difficult to ascertain an absolute safe level for impulse exposure for youth and a more conservative approach may be warranted.

Officials using starter pistols are advised to utilize hearing protection in both ears while firing the pistol. Electronic and newer designs of non-linear attenuation hearing protection may be advantageous for persons firing starter pistols and for individuals positioned near the official. Non-linear devices, such as the E·A·R^® Combat Arms, are advantageous in terms of enabling communication while affording protection from impulse signals (Murphy et al, 2012). Electronic hearing protectors may also be used with radio communication systems via a direct input jack. School systems or other employers of sports officials may be obligated to provide a comprehensive hearing conservation program including noise measurement, noise control, employee training, hearing testing, and hearing protection program components per OSHA 29 CFR 1910.94 or European Union Directive 2003/10/EC (note: other international regulations may also be relevant). Officials using starter pistols are advised to have their hearing routinely monitored and their hearing protectors fit-tested to assure adequate and on-going protection from impulse noise.

The sound pressure levels produced by starter pistols measured in this study are excessive for the purpose of signaling the start of a sporting event. The level recorded at Position A (Figure 5) for the .32 caliber H&R starter pistol shooting blank ammunition was 165.0 dB peak SPL at the shooter’s ear. Based on the inverse square law, the athlete would have to be 90 metres away from the starter in order for the peak levels to be <120 dB SPL and avoid exceeding the WHO impulse exposure limit for children. Adult support staffand bystanders would need to be 8 metres away from the starter in order for peak levels to be <140 dB SPL and avoid exceeding the WHO impulse exposure limit for adults.

The study results confirm that there is a need for hearing protection for the starters as recommended by the NCAA (Kleeman, 2008; Zemper, 2009). However, these findings illustrate that the need for hearing protection extends to people situated within 8 metres (adults) or 90 metres (youth). These distances would be impractical in terms of establishing a perimeter around a starter for a typical athletic event attended by persons of all ages. Additionally, the use of open-barreled pistols as suggested by Zemper (2009) does not eliminate the risk of acoustic trauma and creates additional challenges in terms of weapons permits and the physical presence of a firearm on school properties. Therefore, the use of alternative starting devices may be warranted to minimize the risk to the shooter, athletes, and nearby bystanders during athletic events.

The measurements made in these experiments were conducted outdoors in an environment having no significant reflective surfaces except the ground. While the peak SPL values would be expected to remain similar in an indoor environment, the integrated energy levels (dB L_eqA8) can be expected to increase, and therefore the numbers of permissible exposures can be expected to decrease. Given the sound levels produced by starter pistols, their use for indoor events or when there are acoustically reflective surfaces nearby is of particular concern. Additional research in indoor athletic venues is needed.

The impulsive sounds produced by starter pistols are hazardous to the shooter and others in the immediate vicinity of the shooter. The maximum permissible number of individual shots or MPE are unacceptably few for an unprotected official (shooter). Binaural hearing protection is recommended for the shooter and any nearby event staff. The hearing protection device should afford audibility and provide adequate attenuation for impulse noise. Although the starter pistol can be hazardous and the sounds they produce are excessive for the intended purpose of signaling the start of an event, it does not appear likely that people more than 3 m from the starter would be exposed to enough impulses to exceed the MPE (for adults) used in this study (dB L_eqA8). At the distances included in this study, the risk to athletes appears to be low (when referencing adult MPE criterion), but the sound exposure associated with the starter will contribute to the athlete’s overall noise exposure. The peak levels of starter pistol impulses exceed the 120 dB peak level limit advocated by the WHO for youth when measured at the simulated athlete positions. The use of starting devices with lower level signaling would be necessary to avoid exceeding the 120 dB WHO limit for impulse noise for youth.