Meeting OSHA's confined space warning requirements by reminding workers to follow proper confined space procedures, these high impact polycarbonate signs fit under the manhole cover. The clear material offers a view into the manhole, and ventilation holes allow air out, and water to drain in. Also allows use of instrument probes without removal. Holds up to temperatures ranging from negative 50 degrees to 157 degrees Fahrenheit. Available in two sizes. Custom sizes and signs are available with volume orders.