Turn OFF disconnect, panels turn themselves and array OFF
Without FRSS the array stays HOT
OFF means OFF! Turn OFF disconnect, panels turn OFF.
"The inability to de-energize individual photovoltaic panels exposed to sunlight cannot be overemphasized.  It is absolutely imperative that emergency responders always treat the systems and all their components as energized.  This includes after the emergency event is stabilized, as the system will continue to be energized while exposed to sunlight, possibly with damaged system components that could present serious shock hazards or even cause a rekindling of a fire." Page 53, Fire Fighter Safety and Emergency Response for Solar Power Systems by the Fire Protection Research Foundation
Further reading
With 7,000 panels on a 300,000 sf roof, the Dietz & Watson warehouse fire was a case study for the NEC.
Dietz & Watson warehouse blaze: solar panels hampered firefighting, officials say

NBC channel 10 video coverage of Dietz & Watson warehouse fire
- Kent Kernahan, Locally Grown Power
Simplicity is the ultimate sophistication
FRSS calls for an inherently safe solar module for the mass market.
Mass market solar power will be as safe as a skylight.
Solar power is ready for prime time.

When fire involves a solar array, the fire environment becomes even more complicated.  A damaged and energized array may spread a fire in unpredictable ways or re-kindle the fire after it is out.  Later, damaged, energized solar presents a special risk to demolition or repair crews.
No firefighter wants to stand down and let a building burn, but it happens.
With energized solar, the only sure Personal Protection Strategy available is avoidance of the panels and their wiring.  This leaves firefighters and their command with poor or no choices on how or even if to engage a fire.
Today's problem with solar everywhere
First responders are at risk in 100% of fires where panels are present.  Whether or not the fire has involved the solar panels, first responders must consider them an energized hazard with no way to switch them OFF.
"The inability to shut down the power on these large systems exemplifies the challenge facing fire fighters, since every panel is still generating electricity and thus the wiring and components are always "live" when the sun is shining."
-Page 53
To learn more about the National Fire Protection Association's recommendations concerning fighting solar panel fires, Read Fire Fighter Safety and Emergency Response for Solar Power Systems

"Damaged PV systems are incredibly dangerous. Even when the fire is out, I would not go up there and touch any of that equipment."  22:39 Solar Panel Safety for First Responders part 1.

Matt Paiss, a captain with the San Jose FD, explains in this two part video how to stay alive when fighting a solar panel fire.  Part 1   Part 2

The FRSS indicator is a simplified dial voltage indicator properly labeled and located near the DC disconnect.
FRSS installations may include an indicator to tell the first responder a solar installation can be turned OFF and positive conformation when the array and its cabling are OFF.
Firefighters and other first responders are trained to assess before they engage.  This starts with a hot lap around the the fire site to find and turn OFF all disconnects.  An installation of solar panels implementing FRSS functions exactly as is expected of all other equipment.  It turns OFF. Completely.
First Responder Safe Solar and NEC2014
NEC2014 690.12 "Rapid Shutdown"
DC solar panels without FRSS features unconditionally energize their cables whenever light is present.  The National Electric Code (NEC2014) has continued to concede the inability to shutdown as a limitation in solar technology by allowing all solar panels and cabling within a solar array to remain energized regardless of the position of any disconnects. NEC2014 690.12 mandates that the cables between the array of solar panels and their inverter be de-energized when the disconnect is set to off within ten seconds.  From a practical standpoint, this will typically de-energize the cable that runs up the wall of a building between the ground-mounted inverter and roof-mounted solar array.

Ventricular fibrillation is possible with a one second shock and brain damage may occur within four minutes of heart failure.  In an electrocution in progress emergency, ten seconds may make a successful rescue and resuscitation unlikely or risk the lives of the rescuers. 

The rooftop high-voltage shock-hazard environment within the solar array is unchanged. No cable or solar panel within the array may be safely cut.  Damaged arrays remain energized.
First Responder Safe Solar
FRSS is a superset of Rapid Shutdown.  Each DC solar panel with FRSS features will only energize its cables when an inverter is connected to the solar array.  When the connection between the solar panels and the inverter is opened, because the disconnect is set to OFF or any other reason, all of the solar panels and all of their cabling are de-energized in a fraction of a second. 

In an electrocution in progress emergency, de-energizing in a fraction of a second dramatically improves the opportunity for a successful rescue and resuscitation without risk to the rescuers.

Any cable or solar panel may be cut.  Damaged or disconnected solar panels de-energize themselves. FAIL SAFE.
In a call so many incident commanders have faced before and since, the firefighters had no choice but let the building burn to the ground. In this video posted by NBC10 from early in the fire sequence, the damaged, but still energized solar array burns ahead of the fire consuming the roof.
His call:
"If the building collapses, it collapses…it can be replaced. I'm not sending a man in to lose a life."
On September 3, 2013, a massive 11 alarm blaze broke out at the warehouse in Delanco, New Jersey.  The fully  powered solar array forced Delanco Fire Chief Ron Holt into a bad choice between safety and property.
Early fire. Damaged, energized array.
Safety demands fire fighters stand down.
The aftermath, a total loss.
"Putting a disconnect on a residential roof really does not improve system safety." - Marvin Hamon, PE. A damaged panel can still produce hazardous voltages and currents.  Read more here for industry comments concerning the implementation of Rapid Shutdown.

"The results of the experiment indicate that when illuminated by artificial light sources, such as fire department light trucks or an exposure fire, PV systems are capable of producing electrical power sufficient to cause a lock-on hazard." - Robert Backstrom, Solar Industry Magazine.  A lock-on hazard, where a person cannot remove his hand from an energized circuit, occurs when electrical power is sufficiently great to cause incapacitation due to loss of motor control.  Read more here for more about the issues of energizing PV panels with artificial light.

"AC module systems comply with any new Code language demanding the PV system be shut down to the module level."  - Terence Parker, Solarbridge Technologies
UL tests with standard emergency nighttime illumination show that PV panels still have hazardous current levels.
In a UL fire test that destroyed this panel, a meter shows it's still producing 47 volts . . .
. . . whereas this destroyed panel is still generating over 3 amps.
"Interestingly, the NEC initially wanted to require the Rapid Shutdown function to occur at the module level, but the industry did not have the existing technology to do so." - Natacha Kiler, Sol Systems.  The module is the safest place to cut DC power when an emergency shutoff is activated, because the panel is still energized and capable of producing a safety risk.  Read here for more on industry directions regarding emergency shutdown at the module level, and not at the inverter.
The absence of a comprehensive firefighter safety solution would have the undesirable effect of limiting the growth and success of the solar market.  Some jurisdictions are requiring PV installation margins, or setbacks, from the edge of the roof to allow firefighter access.  A 2 foot margin on a typical 500 sqft rooftop PV installation could reduce its output from 6 kW to 4 kW. "Any changes to setbacks will have an impact on the solar industry." - Susan Jowaiszas, marketing manager for Energy Trust. Read more here.

While it is the solar panels in an FRSS installation that actually shut down the High Voltage DC, it is the FRSS indicator that gives the Firefighter or other First Responder visual conformation.

Normally, the FRSS indicator will follow the position of the DC Disconnect.  ON (Closed) should produce a red indication  and OFF (Open) should produce a green indication.

When the FRSS indicator does not follow the DC Disconnect a potentially dangerous malfunction may exist.  Consult the table on the right.
Please complete the survey.  In addition to providing important input to policy makers, you will be given an opportunity to provide feedback to us on what you think of FRSS.

Typical FRSS installation with standard FRSS markings.