Manufacturing facilities come in different sizes with different equipment and wiring. They use different processes and different materials to manufacture various end products. With hazardous environments, you need to factor in intrinsic safety.
Most manufacturing work environments are quite benign. The materials being used are not hazardous, or poisonous, or caustic or corrosive. They are easy to handle with no additional precautions needed.
But some locations require the use of products that may include combustible materials, flammable liquids, or flammable gasses. These cases require special considerations to avoid any dangerous conditions. The proper safety requirements must be met at all times.
Intrinsic Safety: Definition
Equipment and wiring that is rated as intrinsically safe must not be capable of providing enough electrical or thermal energy to cause ignition in the rated environment. This must be the case for both normal and abnormal conditions. The rating requirements are dependent on the type of environment.
Hazards In A Work Environment
All companies and employees would like the work environment to be perfectly safe in all aspects. This applies to mechanical injury hazards, air quality issues, and other safety concerns. Great effort is expended to reach these goals.
In the US, the National Electrical Code (NEC) defines the nature and levels of the hazards. There are Classes, Divisions, and Groups. The specific classification will determine the required protection techniques.
The Class will define the general nature of the hazard, such as flammable gases, dust, or fibers. The Division denotes the severity of the hazard. The Group indicates the specific type of hazardous material involved.
Any material that can catch on fire and burn is considered to be combustible. Some materials come to mind quickly, such as fuel oil, paint, and kerosene. This includes liquids that have flash points above 100 degrees F.
Others may not be as obvious, such as environments where there are high concentrations of dust in the air. This can be sawdust or dust from coal or various powdered metals. Even a bakery with a high enough concentration of flour dust or a distillery with grain dust can be considered to be at ignitable concentrations. This then will become a combustible environment.
The flash point of a substance is the lowest temperature where enough of it can evaporate to create a combustible concentration of gas. If that temperature is 100 F or lower, it is considered to be flammable. This includes such gases as propane, hydrogen, butane, methane, and ammonia, among others.
Electrically powered industrial equipment is available in tremendous diversity. Some machines are used to mechanically fabricate materials by bending, forming, and stamping. Others are used to formulate an end product by adding ingredients, mixing them, and processing them.
There are instruments that are meant to make different types of measurements. These include length, temperature, pressure, voltage, speed, and scales to measure weights.
Any device that uses electricity is a potential ignition source for hazardous materials that are easily ignitable. This can occur from an electric spark or discharge. It can also occur if there is a fault condition that causes it to improperly heat up. When the temperature reaches a threshold, combustion can happen.
Explosion-Proofing Your Workspace
You must first determine the level of hazard that exists. This will require understanding the Class, Division, and Group. Your environment will be defined by the harshest conditions in that area.
All equipment of all types within this area should be surveyed. This includes everything from light fixtures to handheld power tools, to measuring systems and machinery. Every item must be designed to be intrinsically safe and rated as being approved for your hazard level.
Those items which do not meet the certification level must be removed to a non-hazardous location. Alternatively, if it is not an intrinsically safe device, it must be placed in a suitable explosion-proof enclosure.
How Does Intrinsically Safe Equipment Work
The primary goal of any intrinsically safe item is to limit the energy available that could cause an ignition event. Therefore, it is necessary to determine the amount of energy that is actually available in a device. This is typically the sum of all of the energy-storing components.
The primary devices that store energy include capacitance, inductance, and batteries. The regulations provide formulas that limit the totals of these parameters, dependent on the different classification levels. There are also allowable values of resistors, which prevent significant levels of thermal heating.
Measuring devices, such as weighing scales, can often be powered by batteries. The voltage and capacity of the battery will almost always cause it to fall outside of permissible limits of energy storage. But it is possible to enclose the battery in a small, internal, explosion-proof module. Then you can use fuses and power limiting devices to meet the specifications.
This is the method used by Arlyn for their intrinsically safe scales. Their intrinsically safe platform scales, bench scales and cylinder scales will operate for up to 100 hours or more on a charge. Their intrinsically safe ultra precision scales will operate for up to 30 hours.
These scales are all provided with an extra set of rechargeable batteries. The initial set can be removed after they have been discharged. Then the equipment can continue to run on the second set. Recharging only takes about 4 hours.
Although battery operation may be the most convenient choice in most situations, it is sometimes desirable to provide alternative power. In this case, an approved Zener Safety Barrier may be used to route power to the device. This type of system uses zener diodes and fuses to safely allow external power to be used.
Sometimes, it is also beneficial to have a secondary display indicator in the safe area. Arlyn’s Safety Barrier may also be used for this purpose. Additionally, the secondary indicator can provide multiple communication choices, such as USB, Ethernet, and WiFi.
Creating Explosion-Proof Enclosures
As noted previously, an item that is not classified as intrinsically safe can still be used in a hazardous area. They simply must be inside an approved explosion-proof enclosure. This type of enclosure must be able to withstand the force of an internal explosion within the enclosure. It must contain any such explosion so that it will prevent ignition for its rated Class.
Intrinsically safe equipment is available with a wide range of choices and options. When you need an intrinsically safe scale, contact Arlyn. Their sales staff is trained to provide the appropriate cost-effective solution for any set of parameters.