What does intrinsically safe mean?
Inherently safe means that if something fails it will not cause damage to your device. If something explodes, it won’t explode inside your device.
The intrinsic safety of a product depends on its design and manufacturing processes. There are many factors which influence the inherent safety of a product. These include:
Materials used in the construction of the product (e.g. metal, plastic)
Processing methods used during manufacture (e.g. heat treatment, chemical etching etc.)
Manufacturing tolerances (i.e. how close a part fits to another)
Testing procedures (e.g. test points, burn marks, pressure tests etc.
The concept of “inherent safety” does not exist in isolation. It should be seen in the context of all the other equipment, people and procedures that are used in conjunction with it.
It is important to note that the term “inherent safety” does not mean that a device is completely safe. The user must still ensure that it is used correctly and operated within its design parameters.
The image below shows a simplified representation of how an intrinsically safe product works.
The blue box on the left is the “inherently safe” product.
The red box is a battery which is connected to a control unit. The control unit sends an input signal to the intrinsically safe product.
The yellow box is the intrinsically safe product sending an output signal back to the control unit.
The black box on the right is an external power supply, which provides power to the intrinsically safe product and also protects against electrical spikes and surges.
The intrinsically safe product should always be connected to an ECP. It must not be connected directly to any other power supply or battery.
What is an intrinsically safe product?
As we have seen, intrinsically safe means that the design of a product makes it almost impossible to fail and if it does, the failure is contained within the device.
Intrinsically safe designs and materials do not allow an electrical current to pass through the case of a device. This means that if a fault develops within the device then the internal components are protected.
The advantage of this design is that it makes the device much more reliable and robust. It also makes the device safer to use because the risk of something going wrong is greatly reduced.
It is important to note that all intrinsically safe products must have an ECP attached(explained below). The ECP provides a barrier between the battery and the control circuitry of the product. It is also designed to prevent electrical spikes from damaging any sensitive electrical components.
What does ECP stand for and what does it do?
The ECP stands for Electro-Conductive Protection. The ECP is an electronic device which provides a barrier between the battery and the product’s control circuitry. As such it provides electrical protection to both the battery and the control circuitry in the event of a fault within the product.
The ECP also prevents electrical spikes or surges from reaching the control circuitry and damaging any of the sensitive electronic components. The image below shows a simplified representation of how an ECP works.
The blue box on the left is the ECP.
The red box is the battery.
The yellow box is the intrinsically safe product.
What types of intrinsically safe products are there?
There are a wide range of intrinsically safe products on the market today including:
Lighting products (e.g. emergency exit lights, tunnel lights, miner’s helmets etc.);
Mining equipment (e.g. drilling equipment, conveyor belts, headlights etc.);
Safety equipment (e.g. extinguishers, breathing apparatus, gas detectors etc.);
Test, Measuring & Diagnostic Equipment (e.g. multimeters, oscilloscopes, gas detectors etc.); and
Specialised products (e.g. cable joints, junction boxes, fuses etc.)
Where can I find intrinsically safe products?
Intrinsically safe products are commonly used in a range of industries including:
Mining (e.g. drill bits, mining tools, helmets etc.);
Industrial (e.g. vehicle lights, tunnel lighting, manufacturing equipment etc.);
Utilities (e.g. electrical equipment, lighting, emergency exit signs etc.); and
General (e.g. flashlights, camping lights etc.
Does an intrinsically safe product need to be E marked and do I need to register it?
Yes, an intrinsically safe product must be E marked and registered. It is illegal to sell an intrinsically safe product which has not been E marked or registered.
The E marking is a European Conformity Mark which indicates that the product has been tested and complies with the essential requirements of relevant European Standards.
The registration process is handled by the relevant National Approval Body (NAB). In Ireland, for example, this role is fulfilled by the Irish National Accreditation Service (INAS). This organisation will register any compliant intrinsically safe product which has been tested to the appropriate standard.
What battery designs can be used in an intrinsically safe product?
Batteries can be either Sealed (Maintenance Free) or Vented (Flooded / Refillable).
The two main battery types used in intrinsically safe products are:
Nickel Cadmium (Ni-Cd) batteries; and
Note: The vast majority of intrinsically safe products use sealed (maintenance free) Nickel Cadmium batteries.
What is the typical service life of a battery?
The typical service life of a sealed (maintenance free) battery is typically 5-7 years whilst the typical service life of a vented (refillable) battery is typically 3-4 years.
The reason for the shorter service life when compared to non-intrinsically safe battery is due to the batteries being subject to higher rates of discharge and recharge during use.
What is the typical life of an ECP and how does this compare to normal batteries?
The typical life of an ECP is typically 10 years.
Given that ECPs are typically made up of multiple batteries (packs) which are rated at 3.2V, 18650 Lithium Ion batteries are often connected in series to produce the required voltage (e.g. 12 ECP packs will produce a nominal rating of 12 x 3.2V = 36.0V).
When connected in series, the voltage remains the same but the capacity of each battery decreases. For example:
12 x 3.2V = 36V but each battery is now rated at 3.2/12.0 = 0.25Ah; and
6 x 3.2V = 18V but each battery is now rated at 3.2/6.0 = 0.5Ah.
This means that the ECP will be capable of running for a much longer period of time than a non-intrinsically safe battery.
Calculating the life of the batteries in an ECP:
Number of E-Cells in ECP (n) x Nominal Capacity (mAh) = Nominal Battery Capacity (mAh).
36V ECP with 6 x 3.2V batteries: (n) 6 x 3.2V = 18V x 0.5Ah
36V ECP with 12 x 3.2V batteries: (n) 12 x 3.2V = 36V x 0.25Ah
For the purposes of this example, let’s assume that the average battery is capable of providing a cycle count of 500 before it drops to 80% of its original capacity. From this, we can calculate the number of cycles per year (CY) that a battery is capable of providing.
(n) 500 x 1 = 500
36V ECP with 6 x 3.2V batteries: (n) 500 x 0.5
36V ECP with 12 x 3.2V batteries: (n) 500 x 0.25
Let’s assume that a single battery is capable of running the ECP for 48 hours before needing to be replaced. This means that the system can run for:
500 x 2 = 1000 hours per year.
Over a period of 10 years, we can calculate that the ECP is capable of running for:
1000 hours per year x 10 years = 10,000 hours in total.
The average battery will have a capacity of:
10,000 hours per year x (80% retention) x (80% initial) = 6,400mAh
6,400mAh x 1.2 nominal = 7,680mAh effective capacity.
The average battery is capable of running for:
7,680mAh x 2.4V nominal = 20,360 hours in total.
Over a period of 10 years, we can calculate that the average battery is capable of running for:
20,360 hours in total x 10 years = 204,600 hours in total.
The average battery will have a capacity of:
204,600 hours in total x (80% retention) x (80% initial) = 139,040mAh effective capacity.
What is the shelf life of an ECP?
The shelf life of a typical non-intrinsically safe ECP (without batteries) is typically 5 years. The shelf life of a typical intrinsically safe ECP (including batteries) is typically 10 years.
Does the power source provide the power to the entire system or just the ECP?
The power source provides power to the entire system.
Can the power source also be used to recharge handheld equipment?
Yes, any equipment that can be recharged by a USB connection can also be recharged by the power source.
What happens if there is a short-circuit in an ECP?
This is highly unlikely to happen given that each cell has its own protection circuitry. It is possible but it is rare. It can be eliminated by using batteries that have their own individual protection circuits.
How much does a typical ECP weigh?
A typical intrinsically safe ECP with a power source and without any other attachments will weight approximately 8Kg.
How do you power an ECP?
An ECP requires a dedicated power source. This is to ensure that an ECP is capable of providing consistent power to its attached equipment. An ECP comes with a power source as standard.
Can an ECP be powered from the mains?
No, for safety reasons all ECPs can only be powered from a purpose-designed power source.
How do you know if an ECP is on?
The ECP needs to be turned on at all times for it to be able to provide power to the attached equipment. The ECP will turn itself off if it starts drawing more than its maximum current.
How do you know when an ECP requires maintenance?
All ECPs have an embedded microprocessor that monitors several parameters of the internal circuitry, battery voltage and gives an overall assessment of the condition of the ECP. The operator can see this information on the ECP display.
What are the chances of an ECP over-heating?
This is very rare but it can happen if a user continually runs too much current through an ECP for an extended period of time. If this happens then the ECP will automatically shut down to prevent damage or injury to itself or attached equipment. This means that an operator should turn the ECP off and let it cool down before using it again.
Sources & references used in this article:
- Intrinsically safe telephone (LP Grandstaff – US Patent 4,741,031, 1988 – Google Patents)
- Intrinsically safe telephone (BH Breneman, B Dale – US Patent 5,136,630, 1992 – Google Patents)
- Apparatus for intrinsically safe power interface (RJ Higgins – US Patent 6,902,412, 2005 – Google Patents)