JobHealth Technical HIGHLIGHTS Information for Occupational Health and Safety Professionals What Every M Powered Air Purifying Respirator User Should Know About Batteries September 006 Vol.. No. 6 Geoff Betsinger, C.I.H. Geoff Betsinger is a Certified Industrial Hygienist with the M OH&ESD Laboratory Background M Powered Air Purifying Respirators (PAPRs) are National Institute for Occupational Safety and Health (NIOSH) approved respirators. PAPRs use a power source to run a motor blower that draws or pushes air through a filter. The filtered air is delivered to an inlet covering such as a tight or loose fitting face piece, hood, helmet or head cover. Powered air purifying respirators are generally categorized as belt mounted, face mounted or helmet mounted. Since the wearer does not inhale through a filter the amount of effort expended during breathing is less than when wearing a negative pressure air purifying respirator. NIOSH PAPR certifications cover the entire PAPR system submitted, from the inlet covering, to motor blower, to filter/cartridge. Introduction M Batteries are a key component of a PAPR system since they provide a relatively light weight, mobile power source to run the motor blower. There are a variety of battery chemistries available to PAPR manufacturers. The battery chemistries offered by PAPR manufactures are selected to meet the unique needs of their customers MBatteries are a key component of a PAPR system since they provide a relatively light weight, mobile power source to run the motor blower. while providing adequate power to the PAPR system to meet regulatory requirements. This article provides an overview of battery chemistries commonly used by PAPR manufacturers and is intended as a trouble shooting tool for PAPR users. What is a Battery? A battery cell consists of a positive and negative terminal. Electrons collect on the negative terminal of the battery. Inside the battery, a chemical reaction produces the electrons. There is a wide variety of chemistries used to produce the chemical reaction. The most common chemistries used by PAPR manufacturers are discussed below. The speed of electron production by the chemical reaction (the battery s internal resistance) controls how many electrons can flow between the terminals. Electrons must travel from the negative to the positive terminal for the chemical reaction to take place. Once connection occurs, the reaction starts. Chemistries that are reversible are used in re-chargeable batteries and irreversible chemistries are used in non-rechargeable batteries. continued on page > M JobHealth Highlights Vol.. No. 6 September 006
What Every M Powered Air Purifying Respirator User Should Know About Batteries (cont. from page ) -Electrode Nickel (Ni) Electrolyte Outer Case -Electrode +Electrode +Electrode Cadmium (Cd) Electrolyte gel Potassium Hydroxide Battery Chemistries Battery chemistries commonly used by PAPR manufacturers allow for recharging. Common chemistries currently in use today are: lead-acid, nickel cadmium, nickel metal hydride, and lithium ion. Sealed Lead Acid (SLA) Anode: metallic lead Cathode: lead dioxide Electrolyte: Dilute mixture of aqueous sulfuric acid Features: Lead acid chemistry is a reliable, durable, dependable and well-understood technology. The self-discharge rate is among the lowest in rechargeable battery systems. There are no memory issues and no electrolyte to fill. Lead acid chemistry is capable of high discharge rates. This battery chemistry cannot be stored in a discharge condition. It has a very low energy density, making it very heavy. It cannot be deep discharged very often, and is not environmentally friendly. Nickel Cadmium (NiCd) Anode: cadmium Cathode: nickel oxyhydroxide Electrolyte: aqueous potassium hydroxide Features: This battery has a relatively high number of charge/discharge cycles when properly maintained and has a relatively long shelf life. It may need to be cycled a few times if stored for extended periods. There are generally no transportation restrictions. It performs fairly well at low temperatures and is one of the most rugged battery chemistries available. This is a fairly heavy battery which must be used periodically to prevent memory. It has a relatively high self discharge rate. Most manufacturers are moving away from nickel cadmium chemistries due to environmental concerns. Principles of Battery Charging The barrel represents the battery The height the barrel is above the ground represents the electromotive force which is measuered in Volts Volume of the barrel represents the capacity of the battery which is measured in amp hours Flow of liquid out of the barrel is equivalent to the current draw on the battery which is measured in amps M JobHealth Highlights continued on page > Vol.. No. 6 September 006
What Every M Powered Air Purifying Respirator User Should Know About Batteries (cont. from page ) Nickel Metal Hydride (NiMH) Anode: Rare-earth or nickel alloys with other metals Cathode: nickel oxyhydroxide Electrolyte: potassium hydroxide Features: This battery generally has 0 0% higher capacity than standard nickel-cadmium. Memory is less of an issue with this chemistry than in nickel cadmium. There is minimal regulatory control for transporting this battery and it is environmentally friendly. This battery has a more limited service life and shelf life than nickel cadmium. Storing it in cool temperatures and charging periodically will lengthen its shelf life. Nickel metal hydride chemistry generates more heat than nickel cadmium and requires more complex charge systems to prevent the battery from overheating and being damaged. Self discharge rates are higher than nickel cadmium and the battery should be used at least every three or four months. Lithium Ion (Li Ion) Anode: Carbon compound, graphite Cathode: Lithium oxide Electrolyte: LiPF6, although this has a problem with aluminum corrosion. Alternatives are being considered, such as LiBF. Features: These batteries have a very high energy density and relatively low self-discharge rate. Memory is not an issue with this chemistry and periodic discharges are not needed. Protection circuitry must be in place to maintain voltage and current within safe limits. Large shipments may be subject to transportation restrictions. This battery is much more expensive than nickel based chemistries and is relatively immature technology that is advancing rapidly. Disposal M participates in the Rechargeable Battery Recycling Corporation (RBRC) program which provides for M PAPR batteries to be dropped off (free of charge) at participating recycling collection sites. To find a local recycling collection site, call the RBRC at (800) 8-887. Battery Configurations How do manufacturers get the desired voltage and capacity for their batteries? The solution is to connect individual battery cells in parallel and/or series. Batteries in Series A serial connection means connecting a number of individual batteries in line with the anode of one battery connecting to the cathode of another. If three battery cells with a voltage of.5 volts and amperage of 9.0 are connected in series the final voltage will be.75 with amperage of 9.0. Batteries in Parallel A parallel connection means that battery cells are connected cathode to cathode and anode to anode. If three battery cells with a voltage of.5 volts and amperage of 9.0 are connected in parallel the final voltage is.5 with amperage of 7.0. Batteries in Combination By combining battery cells in parallel and series, manufacturers can obtain the desired power and capacity needed Battery Configurations =. volt.0 amp Series Parallel. volt.0 amp.6 volt.0 amp Combination.6 volt 8.0 amp continued on page > M JobHealth Highlights Vol.. No. 6 September 006
What Every M Powered Air Purifying Respirator User Should Know About Batteries (cont. from page ) mentioned, voltage is the pressure or potential energy of the battery enabling it to move electrons from one point to another. Amps are the number of electrons passing a point at a given time. Adding the voltage of three batteries in a series can be compared to three 0 foot conveyor belts moving 00 pounds of dirt out of a hole. One conveyor moves the dirt 0 feet, the next conveyor moves the dirt 0 more feet, and the last conveyor moves the dirt the last 0 feet. Three conveyor belts moved 00 pounds of dirt thirty feet. In contrast, connecting three batteries in parallel can be compared to three conveyor belt placed side by side. Each can move 00 pounds of dirt 0 feet. The end result is 00 pounds of dirt moved 0 feet. Battery Charging Battery chargers are extremely important in ensuring maximum performance and battery life. Manufacturers face many challenges in developing a charger for a specific battery. Unique features of the battery chemistry, speed of charge, safety, cost and maintenance of the battery cells are the primary factors that go into developing a battery charger. As the speed of charging increases, the complexity of the charger must also increase. In the case of lithium based chemistries, safety circuitry must also be in place. The charger specifically designed for the battery should always be used. Many of the drawbacks specific to the selected cell chemistry are overcome through circuitry in the batteries and chargers. Smart chargers and smart batteries communicate with each other and work in unison to provide an optimum condition to maintain battery service life and prevent dangerous conditions such as thermal overload. Since battery cells are usually placed in series and parallel to achieve the desired power and capacity, a failure of one cell affects the entire battery pack. Some companies advertise that they can refurbish the battery pack. If the company is not the original battery Principles of Battery Charging The large barrel represents the battery charger The height the barrel is above the ground represents the voltage The flow into the small barrel represents the battery charging process Battery capacity is called C It s charging rate is called the C rate manufacturer, you should be very cautious. Most refurbishing centers are not familiar with the circuitry that PAPR manufacturers use. Overriding or removing the electronic components of the battery can cause damage to the cells during recharging and may also be dangerous if safety circuits are removed or altered. M JobHealth Highlights continued on page 5 > Vol.. No. 6 September 006
What Every M Powered Air Purifying Respirator User Should Know About Batteries (cont. from page ) Intrinsic Safety (IS) An electrical device that is intrinsically safe has been certified by an independent testing and certification group such as Underwriters Laboratories (UL). An IS certified electrical device will not generate enough energy to ignite a flammable mixture of the hazard classes specified in the certification. These hazard classes apply to particulates or gas and vapors. Several manufacturers offer PAPR systems that have been certified as intrinsically safe. These systems should be clearly labeled as such. Generally, the labeling is found on the battery; however, the entire PAPR system is evaluated. Hazardous Location Classification The National Electric Code (NEC) categorizes environments into classes, divisions and groups. Class Locations may have flammable gases or vapors present in concentrations that may cause a fire or explosion. Class has two divisions and four groups. Division Flammable atmosphere is expected during normal operations. Division Flammable vapors or gases are handled, processed or used. Generally these flammables are contained and could only be released accidentally. Groups There are four groups of chemicals from the most volatile and explosive to the least. These groups are A, B, C, and D. These chemicals are listed in NFPA 5. Temperature Codes should be referenced for combustible gases and vapors falling outside of the listed groups. Temperature codes are the maximum hazard temperature that an instrument could produce. Codes are listed as T T6; T6 has a lower temperature than T. For example, a chemical not listed in Groups A-D with an ignition temperature of 65 F would allow instruments with T T6 rating to be used (T has a maximum surface temp of 57 F). Class II Flammable due to the presence of combustible dust. Class II has two divisions. Division Airborne concentration of dust may be sufficient to produce a flammable or explosive mixture during normal conditions. Division Airborne concentrations of dust are not normally sufficient to produce flame or explosions. Class III Flammable due to presence of easily ignitable fibers and flyings. Air borne concentrations are not likely to be ignitable. Class III has two divisions. Division Easily ignitable fibers or materials are handled or manufactured. Division Easily ignitable fibers are stored or handled. Battery Service Life Batteries do not last indefinitely. Proper care and maintenance of batteries will help achieve maximum service life; however, even with the best maintenance program, the cell chemistry begins to break down over time. The most common symptom of an aging battery is a reduced run time. A battery that once provided 8 hours of service may only provide 7, then 6 and so on. On-Line Resources There are a number of on-line resources for information on batteries. These links provide excellent information on battery chemistry, service life and chemistry comparisons; however, the first source of information should always be the manufacturer. http://www.batteryuniversity.com http://www.buchmann.ca http://www.powerstream.com Conclusion Batteries provide a mobile power source for PAPRs. This brief overview is intended to provide general information on PAPR battery chemistries and characteristics, and to provide the reader with sources for further information. The first source of information regarding a PAPR system should be the manufacturer s literature, user instructions and technical service. continued on page 6 > 5 M JobHealth Highlights Vol.. No. 6 September 006
What Every M Powered Air Purifying Respirator User Should Know About Batteries (cont. from page 5) Appendix Common Terms Understanding the following terms should help PAPR users better trouble shoot their systems in addition to selecting a system that best fits their needs. Amperage: The number of electrons that pass a given point. The unit of measurement is the Amp or Ampere. Capacity: Electrical energy content of a battery in ampere-hours. It is the time it takes to discharge a battery at a constant current until a pre-determined voltage is reached. Deep Discharge: Discharging a battery below the limit of its capacity. If several cells are connected in a series, there is a risk of stronger cells imposing a reverse polarity across a weaker cell, thus damaging the weaker cell. Many manufacturers have electronics in place that shut down the battery at a certain voltage to prevent deep discharge from occurring. Primary Battery: A battery chemistry that cannot be recharged. The cells undergo an irreversible chemical change during discharge. Secondary Battery: Re-chargeable battery cell. The chemical change is reversible. Cycle: A single charge/discharge of a battery cell. Cycle Life: Number of cycles a battery will typically provide. Generally, a battery is considered depleted when its capacity is less than 60 80 percent. Energy Density: The amount of energy a cell has per weight or volume. This is usually expressed as gravimetric energy (watt-hours per pound/kg) or volumetric energy (watt-hours per cubic inch or cubic centimeter). Intrinsically Safe: A battery with protection circuitry in place. Circuitry minimizes the possibility of an arc or spark occurring. PAPR systems that are deemed Intrinsically Safe are evaluated as a system by test laboratories such as UL or CSA. Memory: Generally refers to a reversible capacity loss in nickel based battery chemistries. Nominal Voltage: Industrial standard for battery cells. For example, nickel cadmium cells have a nominal voltage of. volts and nickel metal hydride battery cells have a nominal voltage of.5 volts. Overcharge: Continuing to charge a battery after it has reached full charge. Excess energy is converted to heat which can irreversibly damage the battery cell chemistry. Smart chargers can be designed to turn off when full charge is reached and cycle a trickle charge at set times to keep the battery fully charged. Passivation Layer: After prolonged storage, a layer may form that must be broken down in order to regain capacity. Cycling the battery several times tends to break down this layer. Reconditioning: Usually only done on nickel based batteries. The battery is deep discharged with a controlled current. This helps to break down large crystals to a more desirable small size, often restoring the battery to its full capacity. This can only be done with specialized equipment. Self Discharge: Capacity loss during storage due to leakage between positive and negative cell plates. Voltage: The electrical potential of the battery. In other words it is the electrical pressure that moves the electrons from point A to point B. References http://www.batteryuniversity.com http://www.buchmann.ca http://www.powerstream.com NFPA 5: Guide to Fire Hazard Properties of Flammable Liquids, Gases and Volatile Solids 99 Edition. Subscribe If you would like to be notified by e-mail when each new issue of JHH becomes available, register at www.m.com/jhh Occupational Health and Environmental Safety Division M Center, Building 5-E-9 St. Paul, MN 55-000 For more information, please contact Health and Safety Services Technical Assistance: -800--60 Fax-on-Demand: -800-66-655 Internet sites: www.m.com/occsafety www.respexam.com M is a trademark of M Company. M 006. All rights reserved.