Deaths of workers in confined spaces are a recurring occupational tragedy. With the proper equipment and training, many of these fatalities can be prevented by atmospheric monitoring.
A confined space is any space that is large enough for an employee to enter and perform work. The space has limited means of entry or exit and is not designed for continuous occupancy. A permit-required confined space has one or more of the following characteristics:
- A hazardous atmosphere (oxygen deficiency, toxic or explosive gases) present or the potential to be present.
- Material with the potential for engulfment is present.
- Inwardly sloping walls or dangerously sloping floors.
- Any other serious safety hazard.
Non-permit–required confined spaces are generic in nature and require the employer to develop and maintain data supporting this determination. Therefore, workers must be prepared for atmospheric monitoring at any given time.
Confined spaces include: trenches, storage tanks, compartments of ships, process vessels, pits, silos, vats, degreasers, reaction vessels, boilers, ventilation and exhaust ducts, sewers, tunnels, vaults, and pipelines.
Construction industry on notice
OSHA is proposing a rule to protect employees from the hazards resulting from exposure to confined spaces in the construction industry. Under the proposed rule, employers would first determine whether there is a confined space at a job site and if there are potential hazards in the space. In the case such hazards exist, the employer then would classify the space according to the physical and atmospheric hazards found in it. The four classifications of confined spaces are: isolated hazard, controlled atmosphere, permit required, continuous system permit required.
The proposed requirements for each type of confined space are tailored to control the different types of hazards.
OSHA first issued the proposed rule in November 2007. The post hearing for this proposed rule was completed in October 2008, and the incoming Obama administration will be driving this forward. This new rule governing the construction industry is expected to go into effect at the end of 2009. Employers will then have a period of time to come into compliance. In the meantime, proactive companies in this industry are already moving toward compliance or at least to 29 CFR 1910.146 requirements.
Selecting a multi-gas monitor
Multi-gas monitors are an essential part of a confined-space entry program. At a minimum, the device should monitor several hazards simultaneously: oxygen deficiency and enrichment; the lower explosive limit (LEL) of a combustible gas or vapor; carbon monoxide; and hydrogen sulfide.
In addition to these gases, a photoionization detector (PID) sensor can be employed in some of today’s multi-gas monitors for protection against a broad range of volatile organic compounds (VOC) such as benzene, xylene and toluene. The airline industry is using this technology for low-level detection of jet fuel.
Today, the best performance comes from a gas monitor equipped with an internal pump and external hose with a hydrophobic filter. The internal pump allows for easy pre-testing of the confined space and limits the amount of accessories involved in the process. Diffusion monitors are still very popular for their small size and cost. External motorized pumps are now a commonly available option. Well-equipped workers often carry a confined space kit. A common kit could include a multi-gas monitor with pump and 10-foot sampling hose for pre-testing, spare batteries, quad-gas cylinder for functional testing and calibration with gas regulator.
Functional test prior to use
Advancements in sensor technology have allowed for longer intervals between calibrations of the monitor, up to 180 days. A functional test prior to each day’s use ensures that the sensors provide an adequate response to gas and generate the appropriate alarms throughout this interval. The two methods used today are:
- Bump test: (qualitative) a functional check that passes a challenge gas over the sensors to activate audio, visual and other alarms
- Calibration check: (quantitative) a bump test using a known concentration of a challenge gas to demonstrate that an instrument’s response to the gas is within acceptable limits.
Increasing in popularity is the use of a docking station that will automatically do the functional test, calibrate, record data and charge the monitors. If evidence of proper maintenance and care of a gas detector is needed, docking stations provide objective proof that procedures are being followed.
Pre-testing and monitoring
Today’s gas monitoring equipment has come a long way from the miner’s canary and is rugged, affordable and easy to use. Workers need to have a personal multi-gas monitor to perform the required atmospheric pre-testing and continuous monitoring. When in doubt, take it out and turn it on.
An atmospheric pre-test of the confined space is required and proper procedures must be followed. Two important factors to be considered are gas stratification and response time.
Gas stratification occurs in a static environment in which a particular gas will “hang out” based on its vapor density. Because of stratification, pre-testing involves taking readings at the top, middle and bottom of the confined space. Make sure adequate time is taken at each interval to account for T90 response time of the sensors (typically less than 30 seconds) and length of hose.
A non-eventful pre-test does not preclude continuous atmospheric monitoring in the confined space. As simple as this sounds, it is not always followed and conditions can change in an instant. An estimated 20 percent of workers fail to use gas monitors properly, if at all. Training is crucial to ensure all workers follow the proper protocol.
Most confined space deaths from atmospheric hazards are preventable. Whether you are new to gas monitoring, or a wellseasoned veteran, confined space recognition and proper instrument use saves lives. Become complacent and you could become a fatality statistic.
