Electronic safety supervision system

By Victor Guerrero A.

The system monitors workers’ presence in the work zone and ensures the presence of safety harnesses that are properly attached to safety lines. Should a worker enter the work zone without a safety harness and without proper attachment to the appropriate safety lines, the system will alarm alerting both the worker and the worker’s supervisor to the danger. This system combined with proper training and supervision ensures that no further accidents will result from improper use of the safety harnesses and safety lines.

“The Electronic Safety Supervision System (ESSS) is designed to protect workers operating on an oil derrick platform by monitoring the proper use of safety harnesses and safety lines”
-Victor Guerrero A.

Background

Workers are required to wear safety harnesses (fall arrest harnesses) while operating on an oil derrick platform fixed at a height of over 100 feet above the ground. The safety harnesses must be attached to retractable fall arrest safety lines affixed to the platform. Unfortunately, either through lack of training or operator negligence, workers may fail to properly use the safety equipment while operating on the platform leading to falls that result in injury or death.

International Engineering Enterprises, LLC developed an electronic safety system to enhance the protection of workers on the oil derrick platform. The Electronic Safety Supervision System is designed to ensure that each worker on the platform is both wearing a safety harness and has it properly attached to the appropriate safety lines.

Overview of System Operation

The system (see Figure 1 below) uses RFID (Radio Frequency Identification) technology and photo-electric sensor arrays controlled via a PLC (programmable logic controller) to monitor workers upon entrance to an oil derrick platform. The system ensures the worker has attached himself properly to safety lines provided for fall arrest. If the worker is not properly protected the system will activate alarms installed both at the control room of the oil derrick and on the platform itself. These alarms notify supervisors and alert the worker to the danger. Several indicating lights are also installed on the platform to communicate to the worker the status of the monitoring system and his level of protection.

The presence of the safety harness as well as the monitoring of the attachment to the safety lines is achieved using RFID technology. RFID tags embedded in the safety harness are activated upon attachment of safety lines to the harness. Interlocks affixed to the safety harness are switched, at the time of safety line attachment, by the worker using keys permanently affixed to each safety line. This causes the RFID tags to begin communicating with an RFID reader (Figure 1 d) installed on the platform. The RFID reader knows which RFID tags are activated and thus knows what safety harnesses are present and what safety lines are attached.

The current system utilizes two zones for worker protection. The first zone requires the presence of a safety harness as well as attachment of the harness to a retractable safety line. The second zone requires the additional attachment of a lanyard to the belt of the safety harness. Entrance and exit into each zone is monitored by the system through "photo-gates" (Figure 1 b,f). The photo-gates utilize three photo-electric sensors to sense the movement of a worker into or out of the work zone. At the entrance to zone 1 a "staging area" allows the worker to attach himself to the safety line before entering into the zone (Figure 1).

RFID Tag Safety Harness

Each system is provided with customized fall arrest harnesses in various sizes. The harnesses meet all the requisite OSHA standards and are customized by the supplier thus retaining all certifications. Customization is required to embed eight active RFID tags evenly throughout the harness and to affix switching interlocks (see Figure 2 below).

Figure 2. Harness

The RFID tags in the customized harness are hidden from view beneath material which protects them and their wiring from damage. Two junction boxes serve to connect the tags with the interlocks and are also hidden from view in Velcro pockets.

Indicators and Alarms

The system uses two alarms which are activated if there is a worker on the platform who is not properly protected. One alarm is installed on the platform (Figure 1 g) to notify the worker and the other alarm is mounted near the control room to notify supervisors. The alarms provide both visual (strobe) and audio indication.

Two indicators communicate the system status with the worker on the platform (one indicator is mounted at each photo-gate) using a tree of three lights (steady red, steady green, and flashing green). When the worker is not attached to the required safety lines for the zone then the steady red light is on. Once the worker attaches to the required safety lines the steady red light turns off and the steady green light turns on informing the worker that the system is ready for him to enter the zone. When the worker enters the zone the flashing green light turns on indicating that the system knows the worker is in the zone. If the worker disconnects from the safety lines while in the work zone, the indicator will switch to steady red and the system will alarm.

Description of System Installation

Each component installed on the platform is housed in a NEMA 4x enclosure ensuring protection against ingress of moisture and dust. The enclosures are made of high strength steel or fiberglass to withstand the industrial environment. Communication and control wires are installed inside flexible water tight conduit joined on the platform by junction boxes. From the platform to the control room level of the oil derrick, the wires are housed inside rigid conduit attached to the oil derrick riser. From the base of the oil derrick riser to the control room where the control box is installed, flexible conduit is used. The control box is also housed in a NEMA 4x enclosure. The control box is fed by a 120 volt circuit protected by a 20 ampere circuit breaker. A key operated latch ensures the control box is accessible only by authorized personnel.