Patent Publication Number: US-2009235568-A1

Title: Firearm Pre-Muzzle Lead Emission Containment Device

Description:
BACKGROUND OF THE INVENTION 
     During recent pre-renovation lead sampling of floor and wall surfaces of a state police forensic ballistics laboratory it was discovered that extremely high levels of lead dust had accumulated in the ballistics lab and were distributed outward to office areas via foot traffic. Typically this type of laboratory is used to discharge firearms recovered from a crime scene into a specially designed water tank (commonly referred to as a bullet trap). In so doing, various characteristics of the firearm and its projectile are recorded into evidence. The bullet traps are designed to recover lead particles released from the muzzle of a firearm. This is achieved by the use of water washing and misting systems or by establishing a negative pressure (vacuum) around the muzzle of the firearm at the port in the water tank where the firearm is discharged. Despite the use of these fully operational systems and dedicated local ventilation, significant lead contamination occurred. Common perception is that most, or all, lead particle emissions travel down the firearm barrel and are released at the muzzle. However, recent testing has shown that lead emissions several times the OSHA Permissible Exposure Limit (PEL) are released from around the gun frame and deposited on surfaces below, despite the use of localized ventilation and muzzle containment. One theory suggests that some level of lead will be deposited on a gun barrel&#39;s internal lans and grooves even when copper jacketed bullets are used. During a bullets travel up the barrel, temperatures vaporize some of this lead deposit and under high pressure (25,000-50,000 psi) emit a portion of this lead vapor rear of the muzzle either as the bullet casing is ejected in the case of a semi-automatic firearm or at the breaching to cylinder joint in the case of revolvers. 
     This condition is highly problematic as high levels of lead (up to 80,000 ug/sq ft) accumulate over time and are tracked out to other areas of the building. Pregnant women working in the lab or nearby offices in particular are at risk. Staff may also take significant amounts of lead home with them on shoes and clothing and contaminate surfaces at home where children may reside. Without understanding this lead emission source it may be difficult to diagnose or perhaps even realize the progressive nature of the lead presence and its effect on remotely exposed children or newborn. 
     The present invention was installed in December of 2007 in several ballistics labs and was found to reduce lead emissions by an average of 98%. Combined with custodial maintenance and cleaning procedures, future lead exposure of this type can be eliminated. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a protection device, which captures lead particles emitted from the ejection port, cylinder to breaching joint, and pressurized surfaces rear of the muzzle on rifles and pistols. 
    
    
     DETAILED SUMMARY OF THE INVENTION 
     The object of the lead emission containment device according to the present invention is to reduce considerably the amount of lead imparted to nearby surfaces by the discharge of a firearm into currently used bullet traps. 
     This object is achieved by a device, which in short, encloses the firearm and collects such lead emissions for proper disposal. The device uses negative pressure within the enclosure in relationship to the environment outside the enclosure. This negative pressure can be supplied by the bullet trap which may already be under negative pressure (i.e. water tank traps) or supplied by a port built into the device to which a HEPA filtered vacuum is attached. This negative pressure has a dual purpose in that it vacuums away airborne particles as they are released, while at the same time creating a rush of make-up air from the front of the device to the rear mounted vacuum port or bullet trap thereby preventing lead particles from making their way out of the enclosure. In the process of collecting the lead particles, smoke and other heavy metals used in bullets or propellants are also trapped. 
     The construction of the device utilizes a clear impact resistant material such as Polycarbonate to allow an unobstructed view of the containment area while imparting additional protection to the shooter against flying debris during a firearm malfunction. An internal metal frame adds additional rigidity and mounting options for connection to various types of bullet traps. A shock absorbing cloth is also attached to the inner side of the frame in the area of the firearm ejection port to prevent damage to the ejected bullet case from striking the enclosure. This is important when forensic examination of the bullet case is needed. The front of the enclosure uses a flexible curtain to allow the user to insert the firearm for discharge while providing some resistance to make-up air entering the enclosure from around the user&#39;s hands. The rear of the enclosure is a solid metal cap with a small hole allowing the muzzle of the gun to pass and discharge the bullet into a bullet trap. 
     Thus, the object of this invention is to contain lead particles released from firearms rear of the muzzle. This object is achieved by a device according to patent claim  1 . 
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     Referring now to the figure, a preferred embodiment of the Firearm pre-muzzle lead emission containment device according to the invention exhibits a construction comprising: 
     A clear polycarbonate cylindrical tube ( 1 ) that is ¼ inch thick, 16 inches in diameter, and 2 feet in length is sufficient to enclose the barrel and receiver of most firearms. The cylinder ( 1 ) is supported at the front and rear opening by a ½ inch thick, 1 inch wide aluminum ring ( 2 ) whose outer diameter is also 16 inches. The cylinder ( 1 ) is attached to the aluminum rings ( 2 ) by 5/32 inch aluminum rivets ( 3 ) which are installed every 90 degrees around the circumference of the cylinder. Entry into the front of the cylinder is restricted by a flexible rubber sheet ( 4 ) that is 1/16 of an inch thick and 16 inches in diameter. The rubber sheet ( 4 ) is cut into ½ inch wide strips at the bottom ⅔ of the sheet to allow the operator to insert the firearm. The rubber sheet ( 4 ) is attached to the front side of the front aluminum ring ( 2 ) with #8×⅜ zinc plated screws ( 5 ). The rear of the cylinder ( 1 ) is covered by a ½ inch thick aluminum plate ( 6 ). This aluminum plate ( 6 ) is attached to the rear side of the rear aluminum ring ( 2 ) using #8×¾ zinc plated screws. The aluminum plate has a 6 and ⅝ inch hole ( 7 ) cut in the center to allow placement of device onto a typical ballistics testing tank firing tube (usually a 6 and ⅝ diameter tube). The plate also has a 2 inch diameter hole ( 8 ) to allow the attachment of a standard High Efficiency Particulate Air (HEPA) vacuum hose nozzle if the ballistics tank to which the cylinder is attached does not have its own negative pressure vacuum. When not in use the hole ( 8 ) is plugged with a #5 rubber stopper. A flexible shock absorbent mesh cloth ( 9 ) is suspended along the interior right side of the cylinder ( 1 ) to prevent ejected bullet casings from striking the cylinder wall and perhaps imparting markings which would confuse forensic analysis. The mesh cloth is attached to the right side of the cylinder by three equally spaced 5/32 rivets ( 10 ) which pass through the top of the cloth and the cylinder wall. The cloth ( 9 ) is purposely not attached at the bottom and is free hanging to allow greater shock absorption.