An Environmentally Robust Proximity Warning System for
	

Hazardous Areas
	

William H. Schiffbauer Gary L. Mowrey, Ph.D. 

Electronics Technician Electrical Engineer 

National Institute for Occupational National Institute for Occupational 

Safety and Health (NIOSH) Safety and Health (NIOSH) 

Pittsburgh, PA 15236 Pittsburgh, PA 15236 

KEYWORDS 

Machinery, Safety, Proximity Warning Systems, Collision Avoidance 

ABSTRACT 

Proximity warning devices can improve workplace safety by alerting workers when they are in a 

hazardous area near moving equipment. Industrial work sites often present extreme challenges to 

safety-based proximity warning devices. Many commercially available types of proximity warning 

sensors and systems can be rendered useless when covered with mud, ice, snow, ore, rock, and other 

material. The list includes radar, ultrasonic, capacitive, and visual types of sensors and systems. 

Addressing these shortcomings, NIOSH personnel have developed a patented active proximity warning 

system called HASARD (Hazardous Area Signaling and Ranging Device) which employs lowfrequency, low-power magnetic fields which are quite impervious to severe environmental conditions. 

A shapeable wire loop antenna which provides the marker of dangerous work areas, has been mounted 

on a continuous mining machine and was mounted inside 1.3-cm thick angle iron. This loop antenna 

was exposed to more than six months of active underground coal production, which included being 

covered by and scraped over with tons of rock, sprayed by a continuous stream of water, and immersed 

in thick mud. After six months the loop antenna showed signs of wear, but was still capable of 

performing its intended function. The HASARD system is now being applied to other industrial 

applications and is showing much promise, especially in harsh environments. This paper details the 

system, describes the tests that have been done, and mentions other areas where it can benefit the safety 

of industrial workers. 
 

INTRODUCTION
	

Researchers at the Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational 

Safety and Health (NIOSH) have been investigating methods and equipment that will provide for the 

safety of workers near moving vehicles and other industrial equipment. Their work was based on a need 

identified from statistical data that highlighted many accidents and fatalities in industrial work settings 

where employees were struck or pinned by moving equipment. The Mine Safety and Health 

Administration (MSHA) database showed that there were a high number of surface and underground 

personnel that were killed when working near machinery and powered haulage (1). For example, 

between 1992 and 1997, there were 24 fatalities just involving continuous mining machines (CMs). 

Another example is that 45 fatalities occur annually with forklifts in the United States. Also, in highway 

construction, between1992 and 1998, 318 vehicle and equipment-related fatalities occurred within work 

zones, where a worker on foot was struck by a vehicle. The victims were as likely to be struck by a 

construction vehicle or a piece of construction equipment as by a passing traffic vehicle. These statistics 

are a small sampling of data that identifies the need for proximity warning systems for protecting 

workers near vehicles and equipment. Many of these fatalities may have been avoided if a reliable 

proximity warning system was employed. 

Addressing the needs of worker safety, NIOSH personnel obtained and tested a variety of different types 

of proximity warning systems to determine their reliability and effectiveness under varying conditions. 

The first tests were focused on underground coal mining. Coal mines have extremely harsh working 

conditions, especially in the coal production area called the face. The primary machine causing injuries 

and fatalities in that environment is called a continuous miner (CM) (figure 1.)

FIG. 1 – CONTINUOUS MINER
	

 First the various 

proximity warning systems were installed and evaluated on a CM and some associated mining 

equipment at the Pittsburgh NIOSH surface test facility. The systems tested were commercial products 

and also one called HASARD that was developed in-house by NIOSH. The HASARD system was 

found to be the most reliable in the underground coal mining environment. Consequently it was chosen 

to be tested under actual coal production conditions in an underground mine near Pittsburgh, PA. The 

system was exposed to water sprays; falling debris, including mud, coal and rocks; sliding sheets of 

rock; extreme vibration; and collisions with walls, and other vehicles B these exposures are normal in a 

coal production section. A few structural changes were made to 

ensure the integrity of the system and the loop antenna. 

The final HASARD system survived for six months under 

typical coal production conditions (2). 
BACKGROUND 

NIOSH personnel reviewed relevant statistics, accident reports, and verbal descriptions for situations 

which have led to worker injury and death caused by moving vehicles and equipment. Some 

commonalities surfaced which could benefit from the application of a properly selected proximity 

warning system. 

Vehicle blind spots 

Most vehicles have blind spots that obscure the driver=s vision. This is particularly true in large 

construction vehicles and haul trucks (3), but it is also very true in much smaller vehicles. Mirrors and 

cameras have been used to minimize the problem, but accidents still occur -- the vehicle operator must 

first see the problem and then react accordingly. Dirty mirrors and lenses, poor lighting conditions, fog, 

and driver fatigue can cause the driver to not see other vehicles and people on foot. An additional 

warning system could be beneficial. 

Vehicle operator unaware of the presence of workers on foot 

Around underground mining machines the work area is very dark and cramped. The operator and his 

helpers have to work in close proximity to the machine. It is normal for the operators to use the walls to 

help to steer the vehicle. Additionally, the vehicles commonly bump into one another when loading and 

unloading ore or coal. Operators are not always aware of the position of their helpers, and/or any other 

person who may be in the work area. A marker on each worker, which is activated as they approach a 

dangerous area, could alert the operator and prevent a potential injury or fatality. 

Vehicle operator unaware of edges of roads 

Accidents sometimes occur when an equipment operator inadvertently contacts the berm along the edge 

of a haul road. The problems have to do with poor visibility and blind spots. A road edge marker could 

provide improved safety. 

Worker fatigue 

Worker fatigue certainly has been a factor in many fatalities. The worker may see the impending 

hazard, but it may not register in his mind. A Awake-up@ call from a warning system may help. 
Improperly marked hazardous areas 

Fork lifts have been involved in many workplace fatalities. Some cases have been attributed to 

improperly marked work areas. Additionally, commonly applied back-up alarms tend to be ignored 

after long-term exposure. Another level of warning needs to be applied. 

Repetition of tasks causing the worker to be unaware of new hazards 

When workers perform a task over and over again it becomes so automatic that the work no longer 

requires concentration. Their minds can drift leaving them unresponsive to dangerous events that could 

occur. 

Each of the cited cases could benefit from a proximity warning system. However, it is very important 

that the proper system is selected for the job, and that the system is reliable in the environment in which 

it is used. It is also imperative that proximity warning systems provide fail-safe features to ensure that if 

the safety device fails, the worker is warned of the failure. If a worker gains confidence in a safety 

system and it fails, the worker and co-workers can be put in jeopardy. An alarm that is always going off 

(nuisance alarms) can also be a major source of danger. It could cause workers to ignore the alarms. 

Maintenance and testing of proximity warning systems should occur on a regular basis to ensure 

confidence in the safety system. 

The first NIOSH application of a proximity warning system was developed for the protection of 

operators and workers around a CM. A number of different types of commercially available proximity 

systems were considered and tested for the job. They included radar, ultrasonic, capacitive, and visual 

types of sensors and systems. Testing proved that for the underground mining application, none of these 

devices were appropriate due to the following and generally common reasons. Any object which got 

into the detection zone would cause the alarm output to trip. This would include the walls of the mine 

and other vehicles which normally come in close proximity to, or in contact with, the machine. 

Additionally, falling coal, rock, and even the water sprays, would set off the alarms. Each of these 

systems could be described as a passive type of proximity system, in that any object in its detection path 

would set off an alarm. Hence NIOSH developed an active type proximity based system (HASARD) 

since no commercially available active type systems could be found at the time. NIOSH has been 

granted a U.S. patent for the HASARD system, Patent No. 5,939,986 (Aug. 17, 1999). 

HASARD DESCRIPTION 

HASARD is an active system. The active feature is very important and is somewhat unique since most 

proximity warning systems (4) are of the passive type. Passive types of systems are triggered by all 

objects they detect within their range which is not always desirable. In surface mining operations large 
haul trucks frequently run over large pieces of earth, rock, and other debris. If the system triggered with 

every large piece of material it detected, it would quickly become a nuisance to the driver of the truck, 

causing him/her to tend to ignore it. In contrast, HASARD, being an active system, can minimize or 

even eliminate nuisance alarms. 

HASARD requires a transmitter on one object and a receiver on another object. In this way, objects to 

be avoided are positively identified and are avoided. In construction sites a HASARD transmitter on a 

large haul truck and a receiver on a worker on foot (WOF) could effectively prevent an accident. A 

transmitter and receiver combination could be put on a wide range of objects such as people, edges of 

roads, poles, etc. HASARD includes a number of accessories to provide remote alarms, data logging, 

and shut-down features. The transmitter creates a current through a properly tuned loop antenna, 

producing a magnetic field about the loop. Figure 2 shows how a magnetic field is produced around a 

conductor.

 FIG. 2 – MAGNETIC FIELD

 The loop acts like any low-frequency transformer. The magnetic field generated is held 

constant due to its constant current design. The loop antenna is usually constructed of one to three or 

more turns of 14 gauge wire. It must be tuned in place to account for the metal in the machines and the 

antenna housing. The magnetic field produced by the antenna is generally referred to as the magnetic 

moment (m) (5). m is the product of the current (I), the number of turns in the loop (N) and the area (A) 

of a current carrying loop. By measuring the resultant magnetic field with a calibrated 3-axis receiver, 

the distance between the transmitter loop antenna and the receiver can be determined. These properties 

are the essence of the HASARD system. The receiver can be made to provide some action (e.g., sound 

an alarm, shut down the equipment, etc.) whenever a magnetic field signal of a certain level is detected. 

From the HASARD perspective, as soon as a person enters a potentially dangerous zone around a 

vehicle, some warning signal or action can be triggered. 

HASARD UNDERGROUND TESTS 

Figure 3 shows a top view of the HASARD system as it was applied to a CM.

 FIG. 3 – HASARD TOP VIEW
	

 The HASARD 

transmitter puts a signal into a loop of wire (the antenna) that is positioned around the periphery
 

of the machine. A HASARD receiver is being held by a worker. As shown, the magnetic field 

generated by the loop conforms to the shape of the loop. The zone indicated is defined by a certain level 

of magnetic signal generated by the transmit loop antenna. The receiver contains circuitry for two 

threshold detectors which are calibrated to trip at signal levels which are relative to specific distances 

from the transmit loop antenna. These threshold detectors are calibrated to identify the zones around the 

CM. The receiver (figure 4) includes a vibrating motor. 

 

FIG. 4 – RECEIVER 

 The motor is triggered by the output of one of 

the threshold detectors when a signal of a certain amplitude is received, which causes the entire receiver 

to vibrate, thereby alerting the wearer. Figure 5 shows how the HASARD system is typically used with 

a CM. 

 

 

FIG. 5 –
	

TYPICAL HASARD SYSTEM
	

Included in the receiver design is a short-range UHF (ultrahigh frequency) transmitter that can 

convey the status of the receiver to a remote data collection point. The data conveyed includes radio 

status, as well as safe, caution, and risk signals. This data can be used to shut down a machine and/or 

turn on the brakes, if required. 

Designing transmit wire loop antennas for HASARD for coal mine use was particularly challenging 

because the antennas had to be protected from much abuse. In order to provide strength and protection, 

1.3 cm thick metal covers were specially constructed. The antenna shown in figure 6 survived six 

months of intense coal production. 

HASARD SURFACE FIELD TRIALS 

The HASARD system was tested for use in surface mining operations. In one case it was evaluated in 

combination with researchers at the Spokane Research Laboratory (SRL) of NIOSH. SRL researchers 

were investigating various sensing and warning system technologies (6) that could be used to detect the 

presence of on obstacle in the blind spot of a large haul truck. The obstacle to be avoided in the SRL 

evaluation was a small pickup truck. HASARD was compared with other types of systems including 

radar, and Radio Frequency Identification Systems (RFID). The SRL study was limited to radio 
frequency devices. For purposes of comparison, this study classified HASARD as an RFID type of 

system, although it might have been more appropriately identified as a magnetic sensing system. The 

testing centered on a 50-ton Komatsu 210 M Haulpak at an SRL surface test facility. While this truck 

was much smaller than most trucks used in surface mining operations, it provided an adequate platform 

for these tests. 

FIG. 6 – ANTENNA 

The system configuration for underground applications of HASARD consisted of putting the transmitter 

and antennas on the CM and placing the receiver on the person. For the surface tests, the transmitter 

was placed on a small truck, and the receiver was placed on the large haul truck. The experiment 

consisted of placing a rectangular loop antenna on the roof of the small truck (figure 7). 

FIG. 7 – SMALL TRUCK LOOP 

 The antenna 

was encased in PVC pipe. The receiver (figure 8) incorporated a simple LED bar graph display that 

indicated the signal strength from 1 to 10, with 10 indicating the strongest signal. 

FIG. 8 - RECEIVER
	

The receiver was used 

to map the detection area. The results of the tests showed that a very uniform detection zone of about 

30 feet could be provided at each corner of the large haul truck. In retrospect, if the transmitter and 

antenna were placed on the haul truck and the receiver was placed on the small truck, the range of 

operation would have increased substantially due to the fact that a larger antenna generates a bigger 

magnetic envelope. The selected test configuration proved that HASARD could be used as an effective 

warning system for surface mining operations. 
 

HASARD has been also employed on a highwall-mining application. A manufacturer contacted NIOSH 

for help in locating an appropriate proximity warning device for their system. The company had tried 

other proximity devices but were unsuccessful in finding one that was reliable. Their system consisted 

of a CM , multiple-car haulage, and a large launch vehicle (figure 9).

 FIG. 9 – LAUNCH VEHICLE

 The problem addressed by 

HASARD was on the launch vehicle. The vehicle included a 40-foot long and five foot wide conveyor 

belt that ran through the center of the machine and was located just below worker foot level (figure 10). 

 FIG. 10 – CONVEYOR BELT
	

In most cases the conveyor belt area was covered by a stacked conveyor section, but there were times 

when that was not so. There was a danger that an operator may be injured by contacting the moving 

belt, or by tripping or falling on to it. To address the problem, a transmit loop antenna was placed 

below the belt and along the length of the launch vehicle. The loop antenna established a danger zone 

over the whole length of the belt. Workers on the launch vehicle were required to wear a receiver. The 

system was designed so that if anyone got close to or fell on the conveyor belt, a radio remote switch 

would be activated via the workers receiver and the belt would be shut off. HASARD=s success 

resulted in the patent being licensed by the company so they could use it on other mining systems. 

OTHER APPLICATIONS 

Industrial work sites experience many fatalities each year. The fatalities are wide ranging and involving 

many different pieces of equipment. NIOSH data has shown that forklifts trucks are one major cause of 

fatalities. Presently most, if not all, fork-lift trucks have back-up alarms. However, accidents are still 

occurring. Perhaps the workers have become oblivious to back-up alarms. The driver of the fork-lift 

can only be sure of avoiding a worker he sees. It=s mainly up to the WOF to avoid the danger. The 

unseen worker could use another level of protection. Implementation of the HASARD system would 

require each WOF to be outfitted with a receiver and a transmitter would be installed on the fork-lift. 

The WOF would receive a vibratory alert when a fork-lift was approaching. The fork-lift operator 

would be alerted to a WOF in close proximity. HASARD could also be used to apply the brakes.
In construction work zones, two-thirds of WOF fatalities, from 1992- 1998 did not involve traffic 

vehicles (7). Of those fatalities, over half involved a backing construction vehicle. Recent events 

indicate an increasing number of fatalities. On June 9, 1998, President Clinton signed into law a federal 

transportation bill called TEA-21, The Transportation Equity Act for the 21st Century (referred to as 

TEA-21). TEA-21 authorized $217 billion in funding over six years. Road construction projects are 

expected to increase by 40%. Addressing their concerns NIOSH recently started a NORA-based 

(National Occupational Research Agenda) research project entitled AEvaluating Roadway Construction 

Work Zones Interventions@ which will focus on minimizing work zone fatalities. HASARD will be 

employed as part of this project. It will be installed and tested on a variety of construction vehicles, and 

will be evaluated for its effectiveness. 

CONCLUSIONS 

NIOSH has created an innovative safety-based proximity warning system called HASARD that has the 

potential to not only warn workers around dangerous vehicles and machinery, but also to shut down the 

vehicle or machine should it pose a danger to the worker. The system was installed in a very harsh 

production environment where it survived for the duration of the project. HASARD has been tested and 

compared to other warning systems and has demonstrated its ability to provide a uniform and reliable 

marker in blind spots around heavy trucks. HASARD has also demonstrated that it can be applied to 

heavy equipment where a uniform marker and machine shutdown capability is needed to keep workers 

out of harms way. HASARD was so successful in this effort that a company licensed the patent for use 

on its other equipment. Other applications to which HASARD could provide a safety benefit include 

use on fork-lifts, and work zones on construction sites. HASARD will soon be tested on haul trucks 

inside of a construction work zone. 

REFERENCES 

1. Schiffbauer, W. H., 1999, AA workplace safety device for operators of remote controlled continuous 

mining machines,@ Am J. of Ind. Med., Suppl. 1. Sept. 1999, pp. 69-71. 

2. Schiffbauer, W. H., 2001, AAn Active Proximity Warning System for Surface and Underground 

Mining Applications,@ SME Annual Meeting, Feb. 26-28, 2001 Denver, Colo. 

3. Johnson, G. A., Griffin, R.E., Laage L. M., AImproved Backup Alarm Technology for Mobile 

Mining Equipment,@ Bureau of Mines Information Circular 9079, 1986, 19 pp. 

4. Jurgen, R. K., 1998, AObject detection collision warning and avoidance systems, Published by 

Society of Automotive Engineers, Warrendale, PA, ISBN 0-7680-0226-5, 1998, 300 pp. 
5. Fink, D. G., McKenzie, A. A., AElectronic engineers=handbook,@ McGraw-Hill, Inc. ISBN 0B7-

020980-4, 1975. 

6. Ruff, T. M., 2000, ATest Results of Collision Warning System for Surface Mining Dump Trucks.@

NIOSH Report of Investigations 9652, 2000, 44 pp. 

7. Pratt, S. G. 2001, AFatalities of Workers on Foot in Highway Work Zones: What are the Hazards?@

Presented at the 2001 International Conference on Roadway Work Zone Safety, May 9-12, 2001, St. 

Louis, MO.