Due to the advancements in Materials Science, new types of substances are being discovered daily. Some of these substances are replacing steel toe caps in the safety boots. The application of science and engineering that studies the behavior of natural and manmade materials. Has brought forth new types of materials to make composite toe caps. Composite toe caps are of 4 types – carbon toe, fiberglass toe, aluminum toe, and titanium toe. We will explore composite and carbon toes, the relationship between them, and their compliance with ASTM Standards.
What is Carbon Toe?
Carbon fibers are 10 times stronger and 5 times lighter than steel. It is eight times lighter than aluminum and 1.5 times lighter. These fibers are 5 – 10 micrometers or 0.0002 – 0.00039 inches in diameter and composed of carbon atoms.
When observed under a microscope, we see that the carbon atoms bond to make microscopic crystals. These crystals align parallel to the longitudinal axis of the fiber. This structure makes them very strong for their size.
Carbon fibers have many forms that have various applications. For example, thousands of carbon fibers are twisted into yarn to make fabrics. These fibers can be combined with epoxy and molded into various shapes. These composite materials can be molded into safety toe caps for work boots.
There are carbon-fiber-reinforced composite materials, too. They are used to making parts for spacecraft and aircraft. They are used to reinforce car bodies, golf shafts, and safety toes in worker’s boots. These materials are preferred because they are lightweight and very strong.
Carbon fiber is classified by its tensile modulus. The British unit is a pound of force per square inch of the cross-section. Low modulus carbon fibers have a tensile strength of 34.8 million psi or 240 million kPa. The ascending order of tensile modulus is – standard, intermediate, high, and ultrahigh. The ultrahigh tensile modulus is 72.5 -145.0 million psi or 500 million-1.0 billion kPa.
In comparison, steel’s tensile modulus is 29 million psi or 200 million kPa. Evidently lighter and stronger, they also have superior fatigue resistant properties. When composited with the right resins, they are the most corrosion-resistant, too.
Carbon toe boots are reinforced structures made of composite material. This material carries a tensile strength of 50,000 psi and a tensile modulus of 3.8×106 psi. It has a compression strength of 42,000 psi, a specific gravity of 1.9, and a Barcol hardness of 70. The carbon fiber is combined with thermoset vinyl ester. This sheet is molded into a toe cap. The carbon fiber content is 63% and the length of each fiber is one inch. The maximum thickness of the toe cap is between 0.1 to 0.25 inches.
Carbon Toe boots are subjected to the same ASTM Standards for Testing and Performance as the Steel and Composite toe boots.
What is Composite Toe?
Composite Toe work boots are lighter than steel toe work boots. They are metal-free, therefore preferred while working with electricity. The boot may be incorporate the composite material in the toe and midsole.
The composite materials may be Carbon fiber, Kevlar, Fiberglass, TPU, etc. It may even employ alloys of aluminum and titanium. These boots are tested for Safety Standards mandated by ASTM and OSHA for the safety of workers. These boots are impact, compression, and puncture-resistant.
The non-metallic composite toe cap is especially useful as they have Conductive, Static Dissipative, Electrical Hazard properties. They are 30% lighter than the steel toe boots, thus cause less fatigue. The other benefits of non-metallic Composite Toe boots are that they are poor conductors of electricity, making them perfect for electricians.
They are poor conductors of heat therefore you are less likely to get hot or frozen toes. They are lighter and spacious. They also pass through metal detectors in security checks on the job site or through airports.
The metallic composite toe boots have caps made of alloys of aluminum or titanium. Aluminum toes are more popular as the alloy is as tough as steel but lighter. These toes are cheaper than titanium toes. Titanium alloy toes are stronger and lighter than steel toes. These boots are 30 to 50 percent lighter than steel toe boots. As these toe caps are thinner, there is more room in the toe box.
Tests and Performance Standards
All safety boots are subjected to
- ASTM F2412 recommends Standard Test Methods for Foot Protection
- ASTM F2413 carries the Standard Specification for the boot’s Performance Requirements for the Protective or Safety-Toe Cap embedded in the Footwear
The gold standard is the ASTM F2413.
ASTM Standards follow an identification code that is placed as marks on various parts of the safety footwear. These codes are;
I/75 denotes Impact Resistance. It is read as Class I/75 footwear. The footwear is supposed to offer a clearance of 1/2 inch for men and 15/32 inch for women’s footwear after an impact of 75 foot-pounds.
C/75 denoted Compression Resistance. It is read as Class C/75 footwear. The compliant footwear is 1/2 inch clearance after being subjected to a pressure of 2500 pounds or more.
This impact and compression resistance will be offered by a Composite or a Steel toe.
Composite Toe (CT) is made of non-metallic or non-ferrous materials. Usually made of an elastomeric material such as Kevlar, carbon fiber, TPU, etc. These are lightweight materials that do not conduct electricity or heat. These toes made of non-conductive elastomeric materials should meet and exceed ASTM F2413-11 Standards.
Steel Toe (ST) is made of non-corrosive metal. This protective toe is at the tip of the boot is supposed to meet and exceed ASTM F2413-11 Standards.
Mt/75 denotes Metatarsal Protection. This footwear has a plate constructed into the upper. This plate can withstand a force of 70 foot-pounds. And offer a 1-inch clearance to the metatarsal area of the foot. If the boot meets this criterion it is said to meet Class Mt/75 ASTM F2413-11 Safety Standard.
Electrical Hazard (EH) Protective boots have shock resistant soles and heels. These boots are said to meet and exceed ASTM F2413-11 Standard when they can withstand 18000V at 60Hz in dry conditions. They will tolerate the current for a minute when there is no leakage or flow over 1mA. The outsole serves as a secondary protection against electric shock. This boot protects the user from accidental contact with live wires, power circuits, energized apparatus, conductors, and parts.
Static Dissipative (SD) boots maintain a sufficiently high resistance to prevent the possibility of an electric shock. The footwear should offer a resistance between 1 – 100 megohms when 50V is applied. Then the boots are said to meet ASTM F2413-11 Standards. According to the ASTM F2413-17 and ASTM F2413-18, there are three types of SD boots;
- SD 100 indicates Static dissipative (1-100 megohms)
- SD 35 denotes Static dissipative (1-35 megohms)
- SD 10 denotes Static dissipative (1-10 megohms)
Slip Resistant (SR) boots are expected to meet and exceed the Mark II Test specified by the ASTM F1677-2005 Standard for Slip Resistance.
Puncture Resistant (PR) boots have plates pressed between the insole and outsole. This plate is supposed to be an integral part of the boot’s construction. If the boot withstands a force of up to 270 pounds through its heel and sole area. It is said to meet the ASTM F2413-11 Standard for puncture resistance.
Boots with composite toe caps or carbon toe caps will be labeled as follows. The label will be printed, embroidered, or pressure-printed on the tongue, gusset, or inside the boot. The information is put in 3 to 4 lines. The fourth line is used only with that section of protection has to be printed. Most of the time the label does not go beyond line 3.
Line 1 – ASTM F2413-18
This line indicates the Standard used – in this case, it is the ASTM F2413 and its date of issuance 2018.
Line 2 – M/I/C
This line indicates the gender the boot is meant for and the type of protection offered. ‘M’ indicates Male and ‘F’ denotes Female. It indicates Impact Resistance and C indicates Compression Resistance.
Line 3 – EH
This line indicates the type of protection offered by the footwear. Here it indicates protection against Electrical Hazard.
Stringent Standards and COC
As new materials, cements, and manufacturing methods are invented daily. The ASTM F13 committee meets every 5 years to update the Standards. They review the needs and requirements of the industries. Then approve the materials and methods to test them. This helps maintain high safety standards.
The three changes in ASTM Standards were made in the year 2018. These changes heralded an improvement in manufacturing processes. This improved the Safety Footwear Standards.
Change 1 – Test Methods for Foot Protection under F2412-18a Standard include detailed diagrams and better-defined test procedures.
Change 2 – The Standard Specifications for the Performance Requirements of Soft Toe Protective Footwear under the Non-Safety/Non-Protective Toe category has been updated to include three levels of Static Dissipation (SD). The labeling will reflect these codes.
Change 3 – A Certificate of Conformance accompanied by a test report from a third party laboratory is mandatory.
By ASTM F2413-18, the third party laboratory has to issue a Certificate of Conformance (COC). This certificate has to include:
- Name of the third party laboratory
- Name of the company the COC has been issued to
- A reference of the manufacturer such as SKU, model, product category, style, etc.
- Certificate issuance date
- Issue date and report number on the Certificate of Compliance (COC)
- Statement – The manufacturer’s reference (SKU, model, product category, style, etc.) meets the performance requirements specified by ASTM F2413-18. The product should have been tested according to the methods mentioned in ASTM F2412-18a besides the list of hazards tested.
The impact has been that the workers get work boots that offer protection in specific types of working conditions. The test methods have improved therefore the results are reliable. And a Certificate of Conformance is required. Manufacturers make boots that meet and exceed performance standards, making for a safer work environment.
Carbon Toe vs Composite Toe
Carbon toe caps are a type of Composite toe caps. There are two types of Composite toe caps – metallic and non-metallic. Carbon toe caps come under non-metallic types.
|Comparative Study of Safety Toes|
|Material:||Metallic/alloy – titanium/aluminumNon-metallic – TPU/Kevlar/Carbon fiber/Fiberglass/Rubber||Aluminum/ Titanium||Carbon Fiber|
|Protection:||Impact, Compression, Puncture||Impact, Compression, Puncture||Impact, Compression, Puncture|
|Other properties:||Impact, Compression, Puncture||Impact, Compression, Puncture||Impact, Compression, Puncture|
|Uses:||Heavy & light industries, production lines, electricity, manufacturing units, electronics, power distribution, etc.||Construction, Heavy Industries, Food Processing, mining, etc.||Electrical works, workplaces with wide thermal fluctuations.
Besides other heavy and light industries.
|Pros:||· Lightweight||· 30-50% lighter than steel toe
· Offer more protection than steel toe
· More room in the toe cap
|· Insulating properties
· Resistant to the flow of electric current
|Cons:||· Less impact & compression resistance||· Compression resistance is less than a steel toe
· Set off metal detectors
· Conductive to electricity & temperature
|· Costly to manufacture
· Bulky toe box
· Toe cap may be compromised after impact
How much weight can a composite toe boot (this includes carbon toe) withstand?
An I/30 and C/30 rated toe can withstand an impact of 30 foot-pounds and a compressive force of 1000 pounds. I/50- and C/50-rated pairs can stand an impact of 50 foot-pounds and a compressive force of up to 1,750 pounds. While an I/75- and C/75-rated pair can withstand 75 foot-pounds and 2500 pounds, respectively.
Do composite or carbon toe boots expire?
Most safety boots last up to one year in an average work environment. They should be checked regularly to ensure they give the protection they are meant for. They should be replaced at any sign of repair.
Do Composite Toe boots have Static Dissipative (SD), Conductive (Cd), and Electrical Hazard (EH) properties?
Composite toe (including carbon toe) boots offer EH, SD, and Cd protection. The Electrical Hazard (EH) boots prevent the possibility of electrocution. They are made of non-conductive materials. Conductive (Cd) boots ground the static electricity. They are made using materials and types of cement that do not offer any resistance to the flow of electricity. They eliminate the possibility of a static shock or discharge which may cause a fire. Static Dissipative (SD) boots resist the flow of electricity. The electric charge drifts through the material, releasing the static charge in a controlled manner.
What are the benefits of a carbon toe?
The carbon fiber toe offers an advanced protection system. The toe meets all performance standards is lightweight and non-conductive. This makes this toe an ideal choice while working with electricity. The material also resists extreme temperature variations of both hot and cold.
What is Barcol Hardness?
Barcol Hardness Test checks the indentation-hardness of a material. This is a very important test to check the impact and compression resistance of a carbon toe boot. An indentor is loaded on to the sample. The indentation and penetration by this indentor are compared with reference material.