Describes the protection provided by hard hats, how to inspect and maintain them.
Reprinted with permission of Construction & Engineering Safety magazine
There's a reason
that construction workers are sometimes called "hard hats." Protective
helmets are often the most obvious form of personal protection that these
workers wear. For most construction jobs today, head protection is required
at all times. Although hard hats come in many different styles, shapes,
colors, and even sizes, all protective helmets are designed to protect
the wearer from serious injury or even death, if they are maintained and
worn properly. Effective protection also depends upon proper care and
use of hard hats.
ANSI Defines Hard Hats
According to the 1997 edition of ANSI (American National Standards Institute) Standard Z89.1, protective helmets are classified as either Type I, top impact, or Type II, top and lateral impact, helmets. Most hard hats are available in both cap, brim in front only, and hat, full brim, models.
Type I helmets, which are tested for top impact and penetration, consist of two basic components working together as a system: the shell and the suspension. The rigid, lightweight shell is designed to deflect objects that hit the top of the helmet. The suspension is engineered to hold the shell in place on the head, but more importantly, the suspension works with the shell to absorb most of the impact energy when something hits the top of the helmet. Because they work together as a system, it is important not to mix components with different sizes or manufacturers. For maximum comfort and protection, the hard hat should be worn straight on the head, with the brim in front. Also, the helmet must fit securely on the head, and the suspension must be adjusted to a snug fit.
According to the classifications of ANSI Z89.1, Type II protective helmets provide the same top-of-the-head protection as Type I helmets, plus limited protection against off-center or lateral blows to the head. This is due to a hard shell, a suspension, and some type of impact energy absorption mechanism, such as a foam impact liner inside the shell working together.
Proving the Effectiveness of a Hard Hat
When the ANSI Z89.1 top impact test is run, the energy that the cap must absorb is about the same as that of a two-pound hammer falling two stories. The hard hat rests on a metal head form that in turn sits upon a pressure transducer that accurately measures the amount of force transmitted through the shell and suspension. When an 8-pound ball makes contact, the shell gives slightly at the point of impact. This takes some of the steam out of the blow, providing the initial protection for the head. Then, the suspension's crown assembly tightens around the head and stretches to absorb the energy within the crown clearance of the cap. All this takes place in about one-fiftieth of a second.
Hard Hat Inspection
Because the protective helmet is a system, if any component is not in good working condition, the hard hat wearer does not have adequate head protection. So, inspecting the helmet before each use is paramount. Inspection is neither difficult nor time-consuming. A thorough job takes less than a minute. The helmet shell should be inspected for cracks, dents, cuts, bad nicks, or gouges both inside and outside. Because even something as small as a hairline crack will widen and spread, helmets with shells showing any damage should be replaced immediately.
Plastic shells such as polyethylene or polycarbonate that are exposed to heat, sunlight, or chemicals can age. The helmet should be replaced at the first sign of damage, long before the color becomes dull, and/or the surface feels chalky. Workers who are struck while wearing a helmet in less than top condition may be seriously injured or killed. The suspension system should be checked for any signs of wear, such as straps that are twisted, cut, torn, or frayed; loose stitching; or plastic parts with cracks or small breaks. Aging from hair oils, perspiration and dirt can cause the suspension to deteriorate and become weak.
One manufacturer recommends replacing the suspension at least once a year, and the entire helmet, at least once every five years. The date the helmet is initially put into service should be noted inside the helmet shell.
Beware of Damaged Hard Hats
The Type I cap described in the ANSI test above was in good condition. When the 8-pound test ball struck the shell, the system worked. But, what kind of protection would a damaged helmet offer a worker on the job? One helmet manufacturer has used a plaster head form to demonstrate graphically what could easily happen when a helmet component is damaged.
The same test was run using a damaged suspension inside the shell. When the ball was dropped on the hard hat worn by the plaster head, the head broke apart. Inspection of this tested hard hat showed that, on initial impact, the damaged suspension snapped, instead of stretching to absorb the blow. This caused the shell and ball to smash down onto the head and crush the model.
The test certainly drives home the importance of inspecting one's helmet before each use. If any part of the system is damaged or worn, workers do not have the head protection they need. This time it was a plaster model, but the next time it could be a worker!
Protective helmets that comply with the ANSI Z89.1-1997 standard for industrial protective helmets will be effective for protection against small tools, bolts, rivets, sparks and similar hazards, in most circumstances. However, some conditions can exceed the helmet's capacity to protect against serious injury or death.
Class E and G helmets provide limited electrical protection as outlined in the ANSI Z89.1-1997 standard. Sample helmets are proof-tested to 2,200 volts for Class G, General, and 20,000 volts for Class E, Electrical. However, these should not be construed as safe contact voltages.
In addition the maximum voltage against which the helmet will protect the wearer depends upon a number of variable factors, such as the characteristics of the electrical circuit, the care exercised in the maintenance of the helmet, and weather conditions. The safe and proper use of helmets in electrical applications should be established by the authority having jurisdiction, and their recommendations must be strictly followed. Most helmet manufacturers recommend that helmet users:
- Store the helmet in a clean, dry area where it is not exposed to extremes of heat or cold, which can affect the helmet's useful service life.
- Clean the protective helmet with a mild soap and warm water to help avoid skin irritation from wearing the helmet.
- Do not stress their helmet by sitting on them or compressing the sides.
- Do not store the helmet on the rear window deck of a car, where the sun can age the shell prematurely. It may also become a dangerous flying object after sudden stops. A protective helmet provides the best possible head protection, if it's cared for properly and replaced when necessary. Workers who understand how their protective helmet system works are more likely to use them properly.
James K. Byrnes is product line manager for MSA, Industrial Head Protection, (412) 967-3144; E-mail: email@example.com.